On a standard QWERTY keyboard, the number 4 is associated with the letter 'r' on the same key. This is because when you look at the keyboard layout, the number 4 appears above the letter R. The symbol '$' is actually on the same key as 4 (when shifted), not '!' (which is with 1) or '%' (which is with 5). The letter 'r' is below 4 on the same key.