need help figuring some things about body fat percentage

Caution - Math ahead.

You weigh 252 lb right now and have 42% body fat. This means that you have about 105.8 lb of fat stored up (because 252 x 42 /100 =105.8). This means that the lean body mass (i.e., muscle, water, bones, organs, and other systems), weighs 146.2 lb (because 252 -105.8 = 146.2). If you want to end up at 22% body fat, you will obviously need to lose weight, but some of the weight you lose will be fat, and some will be lean body mass. This is because some of your lean body mass right now consists of muscles that are getting their work by moving a 252 lb body around, a heart that has to circulate blood throughout it, and bones that have to be strong enough to hold your body together. As you lose weight, this lean body mass will also shrink, as it is getting used less. If you were doing a lot of exercise as you were losing weight, you will lose less of yor lean body mass, but you will always lose some. Let's say that your weight loss consisted of 80% fat and 20% lean mass. Then you would need to get down to 165.1 lb to be at 22% body fat, because at that weight you would have 36.3 fat and 128.8 lb lean body mass, and would have lost 69.5 lb of fat, and 17.4 lb of lean body mass (at an 80% to 20% ratio) from your starting weight to get there. In order to figure out how much you needed to weigh, I had to solve a simple algebraic equation, but I am sure you don't want to learn what that is.

P.S. - This calculation is based on a linear trend with the ratio of fat versus lean body mass staying unchanged throughout the loss phase. I think most research has shown that the more obese you are, the ratio will be skewed higher towards fat loss, and the closer you get to your ideal weight, the ratio will start to skew more towards losing less fat and more lean body mass, until you get down to very low body fat . Then you won't lose any fat, and only lose lean mass.

The 80% and 20% lean mass ratio I used was just an estimate by the way. The best way to do this would be lose the weight and periodically estimate your body fat percentage change using a variety of methods like measurements of body girth at several locations, measurement of skin-fold thickness, or using a bio-electric impedance analyzer. That way you can keep track of the change in lean and fat mass over time.

Unless you're doing it first thing in the morning before anything has passed you lips it's unlikely to give a very good result.

Just keep working hard and results will happen.