We could say that the number of pennies is 2x, nickels are 3x, and dimes are 4x. Adding all of them together, we get 2x+3x+4x=9x. We also know that 9x=1620 because the total amount of coins is 1620. Dividing by 9 on both sides we get x=180. Pennies equal 2x= 2*180=360
