Re: Nice little equation..
Whoever told you to "cross-multiply" should have his mouth washed out with soap. (My views. I welcome others'.)
One step at a time. Don't try to rush. Let the notation help you by WRITING OUT each step. Getting it on paper is WAY easier to organize than trying to keep it all in your head.
(4-x)/(3+x) = 16/25
Multiply both sides of the equation by (3+x), noting that 3+x better not be zero (0). Why is that?
[(4-x)/(3+x)]*(3+x) = (16/25)*(3+x)
Rearrange with appropaite properties of multiplication
[(4-x)*(3+x)]/(3+x) = [16*(3+x)]/25
There is an Associative property to use, now.
(4-x)*[(3+x)/(3+x)] = [16*(3+x)]/25
The answer to my thought question above applies to this step. We need an inverse property for multiplication.
(4-x)*[1] = [16*(3+x)]/25
Simplify
(4-x) = [16*(3+x)]/25
Multiply both sides by 25 (Why don't we have to worry about this being zero (0)?)
(4-x)*25 = {[16*(3+x)]/25}*25
Rearrange with appropaite properties of multiplication
(4-x)*25 = [16*(3+x)*25]/25
There is an Associative property to use, now.
(4-x)*25 = [16*(3+x)]*[25/25]
We need an inverse property for multiplication.
(4-x)*25 = [16*(3+x)]*[1]
Simplify
(4-x)*25 = 16*(3+x)
NOW we get to the Distributive Property of Multiplication over Addition. You'll remember it when you see it. Both sides.
4*25 - x*25 = 16*3 + 16*x
Simplify (Just multiplication)
100 - x*25 = 48 + 16*x
Can you take it from there?
Note: There is no need to jump to the end too soon. See how far we went before we used the "Distributive" hint?
Note: I didn't see any of that vulgar "c------m-----" going on in there.