Use the disributive property to multiply5 (x-9)

Distribute the parenthesis using  > a(b + c) = ab + ac > 5x + 5(-9) > Apply the minus - plus rules > + (-a) = -a > 5x - 5 * 9 < Multiply > 5x - 45

If you are multiply 5(x+9), then you are essentially multiplying 5(x) and 5(9).
The parenthesis just mean multiply.
5 times x equals 5x
5 times 9 equals 45
Because you are subtracting x and 9 in the parenthesis, you're expression would look like this:

5x-45

So, 5x-45 = 5(x-9)

The expression is 5x-45