Question

An operation * is defined by the relation x*y = 5x + 3y - 4xy

Evaluate (3*2)*4

Answer 1

well, 3*2= 15+6-24=-3 check that
then -3*4 must be =-15+12+48=45 check that.

Answer 2

Everywhere you see the * symbol, use the function 5x + 3y - 4xy, where x and y are the numbers to either side of the * symbol.

Order of operations still applies: start within the parentheses first.

3*2 = 5(3) + 3(2) - 4(3)(2)
3*2 = 15 + 6 - 24
3*2 = -3

Now you have (-3)*4

-3*4 = 5(-3) + 3(4) - 4(-3)(4)
-3*4 = -15 + 12 + 48
-3*4 = 45

So the answer is 45.