E=mc^2 m = 3 c = 6 Solve for E please show work so i know how to do this

So me with this math problem. find the value of x the table shows the masses of 50 eggs. mass: 40-44 eggs: 6 mass: 45-49 eggs: x mass: 50-54 eggs: 12 mass: 55-59 eggs: 10 mass: 60-64 eggs: 7 mass: 65-69 eggs: 2 you!

Find the solution of this system of equation -7x+y=-20 9x-3y=36

Emily is entering a bicycle race for charity. her mother pledges $0.90 for every 0.75 mile she bikes. if emily bikes 18 miles, how much will her mother donate?