Kim exercise for 3/4 hours each day for 6 days in a row altogether how many hours does she exercise during the 6 days

Lets calculate how much Kim exercises each day, then we multiply that result by 6 days and we'll have the total.
So each day she exercise 3/4 hours, we could make that division and work with decimals, but lets try it with fractions, because its easier. We have how much time she exercises each day, so we only need to multiply it by 6, that is:
(3/4)(6) = 3*6/4
note how we only multiply the upper part of the fraction, the numerator that is, and leave the lower part alone, the denominator:
= 3*6/4
= 18/4
= 9/2
so she exercises 9/2 hours during the 6 days, that is 4.5 hours, four hours and a half, or 270 minutes.