7k–21+49m Undo The Distributive Property (Factoring)

Can someone pls help

Me answer number 3plz explain how you do it

Evaluate the expression for the given value of the variable 7a - 4a for a =8

Assume that the weights of quarters are normally distributed with a mean of 5.67 g and a standard deviation 0.070 g. a vending machine will only accept coins weighing between 5.48 g and 5.82 g. what percentage of legal quarters will be rejected? round your answer to two decimal places.