Answer:
The distributive property says that when there is a number outside of parenthesis, this means it should be distributed (or multiplied) to the values inside the parenthesis.
So in this situation, 10 x b = 10b
and 10 x 4c = 40 c
so 10(b + 4c) becomes 10b + 40c once the 10 is distributed within the parenthesis.
I hope this helps!