Question 48629
the answer     x= k-15

The "what is" can always be x.

Here are some examples of translating words into algebra.

The sum of x and y         x + y
3 plus a                   3+a or a+3
5 more than m              m+5
b increased by 7           b+7
The difference of x and y  x-y   
4 less than a              a-4
s decreased by 8           s-8
the product of x and y     x.y or xy
5 times a                  5.a or 5a
twice m                    2m
a divided by 6             a/6
the quotient of x and y     x/y