Actually, they paid only 70 riyals. So divide it by 3 : 70/3 = 23.3333. Then 23.333 + 1 riyal each = 24.333. Multiply 24.333 x 3 = 72.999 approx. 73 riyals. Then add the 2 riyals in the waiters pocket, therefore it is 75 riyals.