1/2r - 3 = 3(4-3/2) -----> Simplify the right side.
1/2r - 3 = 3(1/2) -----> Multiply
1/2r - 3 = 3/2 ----> Add 3 to both sides
1/2r = 6/2 + 3/2
1/2r = 9/2 -----> Divide both sides by 1/2 which is the same as multiplying my 2
r = 18/2
r = 9
Hope this helps!