My daughter has a maths question to subtract the area of one rectangle .....one side is 3, the other is x + 1 giving an area of 3x + 3 from a larger rectangle...one side is 5(2x - 1) the other side is x giving an area of 10x - 5 times x which hopefully equals 10x sq - 5x??? How does she subtract 3x + 3 from 10x squared - 5x ??