carcass wrote:

X is the first mile and y are the additional miles

So, 1*x + y * 9 (9 because we have the additional miles less the first mile X 10 - 1 = 9 )

1)x + 9y = 0.90 + 8y ( we can't solve) INSUFF

2) x + 9y = 1.20 + 6y INSUFF

1) + 2) we can subsistute and solve

C should be the answer

The answer is correct, it is C.

Just something to consider: when you are already given the variables -

f and

m the prices in cents for the first mile and the additional miles, respectively, no need to define new variables, just to have the prices in dollars.

And I wouldn't suggest just picking automatically the

x and

y variables when dealing with some quantities with some specific meaning.

f from

first and

m from

miles are suggestive.

With

f and

m your two equations would be:

f+9m=90+8m f+9m=120+6m _________________

PhD in Applied Mathematics

Love GMAT Quant questions and running.