Can someone me with my quadratics and equations questions? i need to show my work : )

Y = x^2 +2x
y = 3x +20

so: 
x^2 + 2x = 3x + 20

subtract 3x from both side:

x^2 +2x -3x = 20

combine like terms:
x^2 -x = 20

subtract 20 from each side:
x^2 -x -20 = 0

factor the polynomial:

(x-5) (x+4) = 0

solve for x
x = 5 and x = -4  ( 5-5 = 0 and -4 +4 = 0 )

replace x = 5 in 2nd equation:  y = 3(5) +20 
y = 15 +20 
y = 35

replace x with -4 in same equation:
y = 3(-4) +20
y = -12 +20
y = 8
 so solution is (5,35) and (-4,8)

The answer is 10. sorry i was wrong the 1st time