This week, I got half of the question correct, since my final answer was . However, the actual answer was
and I could not figure out why. While I was going over the homework with my friends and discussing this one question, the solution suddenly popped into my head and the question finally made sense!
I had been adding and multiplying the exponents together, but that was only half the battle:
But the exponent meant that the binomial is multiplying by itself, so using distribution to solve the problem is the correct way to do it: