Ok first when showing exponents you use carrots "^" and to solve this you multiply both sides so:
5x^2*3x and 5x^2*9= 15x^3+45x^2
-2x*3x and -2x*9= -6x^2-18x
-5*3x and -5*9= -15x-45
Now you solve the problem: 15x^3+45x^2-6x^2-18x-15x-45
15x^3+39^2-33x-45 and that is your answer! C
I hope this answer helps!