Step-by-step explanation:
Multiplication of fractions is easiest operation. Simply multiple numerator to numerator and denominator to denominator. For example,

Addition and subtraction requires that we find a common demoninator.
For example,

The common denominator is 12. So I need to muliply each fraction to get the right denominator. 4*3 = 12.

Then we add the numerators

Then we should reduce.

Division is a little trickier because we have to flip-flop the second term and then multiply. For example: 
Thee answer is 25. 25 is a square number as it is 5 times 5. The sum of the digits 2+5 is 7.
V=4/3 πr^3would be the formula
The square root of Pi is approximately 1.77245.
If so, start by factoring the numerator. Then cancel any common term in the numerator and denominator. If you end up with no denominator, then use the original denominator. Set it equal to zero and solve for x. That value of x will be the restriction.