The answer is 14.60. Hope this helps!
Let's assume two variables x and y which represent the local and international calls respectively.
x + y = 852 = total number of minutes which were consumed by the company (equation 1)
0.06*x+ 0.15 y =69.84 = total price which was charged for the phone calls (Equation 2)
from equation 1:-
x=852 -y (sub in equation 2)
0.06 (852 - y) + 0.15 y =69.84
51.12 -0.06 y +0.15 y =69.84 (subtracting both sides by 51.12)
0.09 y =18.74
y= 208 minutes = international minutes (sub in 1)
208+x=852 (By subtracting both sides by 208)
x = 852-208 = 644 minutes = local minutes
