(-3/4n + 3/8)
Distributive property is multiplying the number outside of the parenthesis by the numbers inside. You should likely review multiplying fractions. (You will multiply the numbers across and then simplify further.)
For example:
1/4 times -3n...
1/4 remains the same, -3 becomes -3/1. Multiply the numerators and denominators and you get -3/4, or in this case -3/4n.