First I would set up how i was taught using Pascals Triange. As this is to the power of 4 the numbers across will be 1 4 6 4 1.Then I would multiply each number by the correct power of either (-5x) or (1). As I know that if (-5x) is to the power of 2, 1 must be to the power of 2.
This gives me (1 * (1)^4 * (-5x)^0) + (1 * (1)^3 * (-5x)^1) + (1 * (1)^2 * (-5x)^2) + (1 * (1)^1 * (-5x)^3) + (1 * (1)^0 * (-5x)^4).
Anything to the power of 0 is 1 and using this I get the answer1 - 5x + 25x^2 - 125x^3 + 625x^4