Exponents:
x³ = x * x * x
x³ * x² = x³⁺² = x⁵

 Combine like terms:
3x + 2y + 5x - 9y = 8x - 7y

 Multiplication distributes over +, -
3 * (2x - 4y + 5) = 3*2x - 3*4y + 3*5
= 6x - 12y + 15