Problem Solving

Can not understand the answer, can some one please explain the answer

you can solve this question by using equation--

0.6 + 0.06(x-7) = 0.08x

X= duration in minutes.

Under plan A cost is 0.6 + 0.06(x-7)

Under plan B the cost is $0.08X

since the amount needs to be equal as stated solve for X .

X=9

OA

9

A certain telephone company offers two plans, A and B. Under plan A, the company charges a total of $0.60 for the first 7 minutes of each call and $0.06 per minute thereafter. Under plan B, the company charges $0.08 per minute of each call. What is the duration of a call, in minutes, for which the company charges the same amount under plan A and under plan B?

A. 2
B. 9
C. 15
D. 21
E. 30

Under plan A, the cost of the first 7 minutes = 60 cents.
Since plan B charges 8 cents per minute, the cost of the first 7 minutes under plan B = 7*8 = 56 cents.
Plan B needs to catch up by 4 cents.

We can plug in the answers, which represent the total time required for the two plans to charge the same amount.
After the first 7 minutes, the difference between plan B's rate and plan A's rate = 8-6 = 2 cents per minute.
Since plan B is behind plan A by only 4 cents, it will not take long for plan B to catch up to plan B.
Thus, answer choice B -- which implies that only 2 additional minutes are needed -- seems almost certain to be correct.

Answer choice B: 7 minutes + 2 additional minutes
Total cost for plan A = 60 + 2(6) = 72.
Total cost for plan B = 56 + 2(8) = 72.
Success!

The correct answer is B.