7+4(3a+5b)
To distribute 4 into the parentheses, multiply it to each term in the parentheses.
We can see that the terms inside are 3a and 5b, and after we multiply them by 4, we would get 12a and 20 b.
Because in the parentheses, 3a and 5b are originally being added, we also add them after we distribute 4 into the parentheses.
7+4(3a+5b)
=7+12a+20b
Now, we cannot combine like terms, since we only have one term with each variable, a and b. 7 is not being multiplied to a variable so we cannot combine that with anything either. In other words, we cannot combine like terms after the first step since there are no like terms to combine.
I hope this helps!