A typical monthly water bill in Bellingham consists of a fixed fee, plus a charge for each $100$ cubic foot (ccf) of water used. $1$ ccf ($100$ cubic foot) = $748$ gallons. A household using $10$ ccf is billed $\$54.92$ whereas a household using $15$ ccf is billed $\$65.77$.
How much water is used by a household that incurs a bill of $\$100$? Round to $2$ decimal figures and use ccf units.
I am confused since $54.92/10$ and $65.77/15$ are different amounts, so the cost per $1$ ccf is different for each. help??