A tank and a pail contain a total of 5136 milliliter of water. Jacob pours 314 milliliters of water from the pail into tank. The amount of water in the tank is now 7 times what is left in the pail. How much water was in the pail at first?

Let t = mL water in tank

let p = mL water in the pail

Start with the first statement

t + p = 5136

Second statement

7 (p - 314) = t + 314

Use substitution to re-write as one equation in one variable.

t = 5136 - p

7 (p - 314) = 5136 - p + 314

7p - 2198 = 4822 - p

7p + p = 4822 + 2198

8p = 7020

p = 7020/8

p = 877.5 mL