Question

Can someone please tell me why I got this wrong?

Answer 1

We have 
f(x)=−x²+ 5x + 6
g(x)=3x − 2

we know that
f(x)=g(x)
the solution is the intersection both graphs

using a graph tool
see the attached figure

the solution are the points
(4,10)
and
(-2,-8)