If 6x^2 +7x = 90 and 6x^2 -7y = 20, then what is the value of 12x +12y

I have to show work too and i dont get it. Elimination or sub?? I dont know I need help. Please show work

6x^2 +7x = 90
=>6x^2 +7x -90=0____1
6x^2+27x-20x-90=0
=>3x(2x+9)-10(2x+9)=0
=>(2x+9)(3x-10)=0

x=-9/2,10/3

from these two values of x we can find two values of y by using eqn
6x^2 -7y = 20___2

put x=-9/2 in eqn 2

6(-9/2)^2-7y=20
=>121.5-20=7y
=>y=14.5

so
12x +12y=12*(-9/2)+12*14.5=120 ans.....1


now put x=10/3 in eqn 2


6(10/3)^2-20=7y

=>y=20/3

so ,12x +12y=12(10/3+20/3)=120 ...ans


thank you...