Given that a phone call is charged x cents in the first minute and y cents from the second min onwards. How many minutes did a person speak, if his bill is $4.94?
Not enough information. He could be charged 494 cents for the first minute, then he spoke 1 minute; or he could be charged 493 cents for the first minute and 1 cent for the second minute, in which case he spoke two minutes, and we can find examples all the way until 495 minutes, assuming x and y are non-negative integers.
Actually, if x = 494 and y = 0 then he could have spoken any number of minutes > 0.
Maybe this is an exercise in literal equations? If we say that t = time spoke in minutes, the equation could be written as
$\displaystyle x + y(t - 1) = 494$
(using cents as the unit)
You can still solve for t like this:
$\displaystyle \begin{aligned}
x + y(t - 1) &= 494 \\
y(t - 1) &= 494 - x \\
t - 1 &= \dfrac{494 - x}{y} \\
t &= \dfrac{494 - x}{y} + 1
\end{aligned}$