remember, you can do anything to an equaiton as long as you do it to both sides
15.
times both sides by 4
3(x-7)=4(x-2)
distribute
3x-21=4x-8
minus 3x both sides
-21=x-8
add 8 to both sides
-13=x
x=-13
16.
distribute -1
7x-1(5x-1)=2
7x-5x+1=2
2x+1=2
minus 1 both sides
2x=1
divide 2
x=1/2