First of all, you are using the wrong row number of the triangle. The top row is 0, and the second row would be 1, and so on. Remember that the exponent of the expression would be the row number. In this case, the exponent of the expression is 4, so you should have 5 terms.
Second of all, since you are subtracting in the expression, your signs should be alternating.
That's why my answer wasn't coming out right. Thanks Ms. Thompson!
No problem Olivia! And remember the power laws, especially since you have a power of a power, so you need to multiply them together.