# Question Video: Solving Problems Involving Linear Relationships Mathematics • 7th Grade

A water company bills its customers using the rule 𝑐 = 10 + 4𝑚, where 𝑐 is the cost in dollars, 𝑚 is the number of cubic meters of water used, and 10 is the standing charge. They produce a bill for \$262. How many cubic meters of water have been used?

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### Video Transcript

A water company bills its customers using the rule 𝑐 equals 10 plus four 𝑚, where 𝑐 is the cost in dollars, 𝑚 is the number of cubic meters of water used, and 10 is the standing charge. They produce a bill for 262 dollars. How many cubic meters of water have been used?

We’re given the rule or equation 𝑐 is equal to 10 plus four 𝑚. We’re also told that the cost 𝑐 is equal to 262 dollars. This means that we can rewrite the equation as 262 is equal to 10 plus four 𝑚. This equation can then be solved using the balancing method. We begin by subtracting 10 from both sides of the equation as subtracting 10 is the opposite of adding 10. 262 minus 10 is equal to 252, which is equal to four 𝑚. Our second and final step is to divide both sides of this equation by four. 252 divided by four is equal to 63. And four 𝑚 divided by four is equal to 𝑚.

One way of calculating 252 divided by four would be to use the short division bus stop method. Four does not divide into two, so we carry the two to the tens column. 25 divided by four is equal to six remainder one. So, we carry the one to the units or ones column. Finally, 12 divided by four is equal to three, so 252 divided by four is equal to 63. We can therefore conclude that 63 cubic meters of water have been used.