Pls help I need to get my grade up

When eating out, record the total cost of your meal (before tip) and the tip that you left. determine the percent of the cost of the meal that you left as a tip.

Acollection of coins has value of 64 cents. there are two more nickels than dimes and three times as many pennies as dimes in this collection. how many of each kind of coin are in the collection?

How to find the exponential function y=ca^x, with points (1,2) and (2,1)