A person swims 11 miles downstream in the same time they can swim 7 miles up stream. The speed of the current is 4 miles per hour. These situations can be represented by the equations
Downstream: t=11/s+4 Upstream:t=7/s-4,
where t stands for time and s is the speed of the swimmer. What is the speed of the swimmer swimming in still water?

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.