Answer: 920.3 ft
Step-by-step explanation:

Excel expects a + or = sign before math calculations.
Also, for arguments of functions (such as sqrt), parentheses "()" are used. Brackets "[]" are not acceptable.
That leaves only one remaining option.
13. Because it can't be divided by a whole number except 1 and itself. 14 can be Divided by 2. 21 and 33 can be divided by 3 making them composite or divisible by more than just 1 and itself :)