How many gallons of bleach are in x gallons of a 70 percent bleach solution?

7x/10 (That's 7/10 times x). So if x = 10 gallons, then there are 7 gallons of bleach in the solution. (7gal/10gal = 0.70 = 70%). This answer if correct if the percentage is by volume. Otherwise, the question can not be answered without knowledge of the basis of the percentage.