you can translate this phrase into a mathematical inequality:
"the sum of a number y and 9 is at least -1" means y + 9 ≥ -1
if you wanted to take it one step further you could isolate the y variable to solve the inequality by subtracting 9 from both sides
y + 9 ≥ -1
y ≥ -10
meaning that any number "y" that is -10 or greater will satisfy the condition