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.
ANSWER
The correct answer is C
EXPLANATION
We want to find the value of

This is the same as:

We cancel out the common factors to get:

We simplify to get:

The correct answer is C
0.018 will be 18/1000 = 9/500
1/10 is left.
Explanation:
First we need to find a common denominator. Since 5×2=10, if we multiply 4/5 by 2/2, we will be able to subtract that from 9/10.
4/5×2/2= 8/10. Then if we subtract that from the 9/10 left of the pizza, we get 1/10, the amount remaining.
Hope this helps :)