for this, all you have to do is take your info and make it an equation. x will represent the number
"quotient of a number" = you'll have to divide
"a number and -9" = (x/-9)
"increased by 10" = add 10
"is 11"
so just put those separate parts together:
(x/-9) + 10 = 11
then solve:
(x/-9) = 1
multiply both sides by -9 to isolate x
x = -9