Part A.
P is the amount Emma borrows: $300
r is the annual interest rate, expressed as a decimal: 0.15
n is the number of compoundings per year: 12
Part B.
Evaluating the formula with t=4, you have
P(1 +r/n)^(nt) = 300(1 +.15/12)^(12*4)
= 300(1.0125^48)
= 544.61
Emma will owe $544.61 in 4 years.