Jack can program an app in 9 hours. Chris can progam the same app in 2 hours. How long would it take them to program the same app working together?

The pie is multyplued by the second step

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.