Answer:
20x⁵ + 20x⁴
Step-by-step explanation:
Use distributive rule: a*(b +c) =a*b + a*c
5x⁴(4x + 5) = 5x⁴ * 4x + 5x⁴ * 5
= 20x⁵ + 20x⁴
Hint: 5x⁴ * 4x multiply the coefficient and then the variables. For multiplying variable, if they two have same base, then add the powers
5*4 * x⁴ * x = 20x⁵
