Question 301114
Just use the distributive law.

In other words, multiply 5 by every term inside the parentheses.

5(2a - 1b + 3a) = 10a - 5b + 15a

We now combine like terms.

Final Answer: 25a - 5b

NOTE: There is no reason to place a 1 in front of any variable.

For example, the middle term in the parentheses given to your son 1b can also be written as b.  Both terms mean the same thing.