front end estimation requires you to take the front / first digit of each number in this expression and round.
if you don't know how to round, basically you take the next digit after the first one, (in 719 you take the 1) and determine if that's below or above 5. If below, then keep the original first number. If above, add one more to the first digit. If the number is five itself, it is most common to round up (so add one).
like 425 would round to just 400; and 676 would round to 700.
