We'll be using y as the answer, pay attention and this'll
help you alot in Algebra I and II. We're going to try to isolate x.

1^st Problem: 3x+5 = y
3x+5 = y
3x = y-5
x = (y-5)/3

2^nd problem: 5-x²+12 = y
5-x²+12 = y
17-x² = y
-x² = y-17
x² = 17-y
x = Square_Root(17-y)

3^rd problem: 3x+x-10 = y
3x+x-10 = y
4x-10 = y
4x = y+10
x = (y+10)/4

4^th problem: 8x*5x-20x² = y
8x*5x-20x² = y
40x²-20x² = y
20x² = y
x² = y/20
x = Square_Root(y/20)

5^th problem: 19x-3²x+5 = y
19x-3²x+5 = y
19x-9x+5 = y
10x+5 = y
10x = y-5
x = (y-5)/10

6^th problem: (x-7x+x^2)/(2x) = y
(x-7x+x^2)/(2x) = y
(x-7x+x^2)/x = 2y
1-7+x = 2y
x-6 = 2y
x = 2y+6
x = 2(y+3)

7^th problem: (x-5x+10)/(2+x) = y
(x-5x+10)/(2+x) = y
(10-4x)/(2+x) = y
10-4x = (2+x)y = 2y+xy
-4x = 2y+xy-10
x = (-2y-xy+10)/4
Guess and Check ?

8^th problem: x-8+10x² = y x-8+10x² = y
x+10x² = y+8
x(1+10x) = y+8
x = (y+8)/(1+10x)
Guess and Check ?

9^th problem: (x-8)²/(3+x) = y
(x-8)²/(3+x) = y
(x-8)² = y(3+x)
x²-16x+64 = y(3+x)
x²-16x = y(3+x)-64
x(x-16) = y(3+x)-64
x = (y(3+x)-64)/(x-16)
Guess and Check ?

10^th problem: (x+3)/(x/5) = y
(x+3)/(x/5) = y
5(x+3)/x = y
5(x+3) = yx
x = (5(x+3))/y
Guess and Check ?

In these problems x will always be a whole number between 1 and 100.