If the amount of time to prepare and deliver a pizza from MOD PIZZA is normally distributed with a mean of 20 minutes and standard deviation of 5 minutes. Determine the percent of pizzas that were prepared and delivered:
(a) Between 20 and 25 minutes (b) In less than 18 minutes
( c ) If MOD PIZZA advertises that the Pizza is free if it takes more than 30 minutes to deliver, what percent of the pizza will be free?

I need to answer a, b and c - it is not mutiple choice. I also need to show all relevant steps and plus I really want to understand how to do this! I am completely stuck on this one and its due tonight. Please help!! :) Ill give badges, brainliest, thanks, all of that for whoever can help me!