help with another math problem.

<li>A telephone company charges x cents for the first
minute of a call and charges for any additional time
at the rate of y cents per minute. If a certain call
costs $5.55 and lasts more than 1 minute, which of
the following expressions represents the length of
that call, in minutes?
(A) 555- x/y
555+ x- y/y
555- x+ y/y
555- x- y/y
(E) 555/x+y</li>

<p>Why is the answer C?</p>

<p>For the first minute, x cents are charged
Suppose the total call duration is D min.
number of minutes that would be charged y cents per minute is D-1</p>

<p>x+ (D-1)y= 555
D-1 = (555-x)/y
D= (555-x+y)/y</p>