Should be C. ( I need to add more characters so hi )
Answer:
y=3x.........1
y=x^2-10.......2
substituting value of eq 1 to 2
3x=x^2-10
x^2-10-3x=0
x^2-3x-10=0
x^2-5x+2x-10=0
X(x-5)+2(x-5)=0
(x-5)(X+2)=0
then
X=5 or X=-2
again
y=??
when X=5
y=3×5=15
when X=-2
y=-6
