How do i do this on my calculator 72.5 - 70 divided by 3 divided by .5?

Cody was 165cm tall on the first day of school this year, which was 10% taller than he was on the first day of school last year.

There are three bags: a (contains 2 white and 4 red balls), b (8 white, 4 red) and c (1 white 3 red). you select one ball at random from each bag, observe that exactly two are white, but forget which ball came from which bag. what is the probability that you selected a white ball from bag a?

Which of the following is the best first step in solving the equation below? 4+2㏒³x=17