Determine the constants A and B so that the similarity becomes an identity.
A(4-x)+3x=B(9+2x)
Some help would be great thanks!
no idea at all?
just expand it out to start with
$4A -Ax + 3x = 9B + 2Bx$
for an identity this must hold true for all x. So equate the constant bits and equate the bits multiplying $x$.
$4A=9B$
$3-A=2B$
Do you understand this? If not stop and look at it until you do.
Now we have two equations and 2 unknowns and use your favorite method to solve this system of equations.
You should know how to do this so I'm going to leave it to you to finish.