1 gallon (it’s stayed in the question)
10^-10 in decimal form is 0.000000001. Because the exponent is negative, you move the decimal point ( decimal point is at the end of 0 of the base number 10) 10 place to the right of 10 and u get the answer above. I discarded the 0 later in the answer because now that you've moved the decimal, that 0 have no value. But when forming it in decimal you have to use that 0 or you will get a wrong answer, instead of eight 0's, you will end up with nine 0's.
