Question

A phone company charges $0.06 per minute for local calls and $0.15 per minute for international calls. When your bill comes, it states that you accumulated 852 minutes with a charge of $69.84. Write and solve a system of linear equations to find the number of local and international minutes used

Answer 1

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