Let's translate the sentences they give us:
"Nine times the sum of a number and eleven is -108. "
The sum of an unknown number (let's call it "x" ) and eleven, can be written as:
( x + 11)
Now,nine times this is the product of 9 times the quantity we just found:
9 * (x + 11) = -108
now we use distributive property to eliminate parenthesis;
9 x + 99 = -108
now we subtract 99 from both sides to isolate the term in x:
9 x = -108 - 99
9 x = - 207
Now we divide both sides by 9 in order to leave the unknown by itself:
x = - 207/ 9
x = - 23