Answer:
The phrase "a number decreased by -4" can be simplified to "a number plus 4", since subtracting a negative number is the same as adding a positive number. So we can rewrite the sentence as:
"A number plus 4 is at most 9."
Using algebra, we can solve for the possible range of values for the number:
Let x be the number.
x + 4 ≤ 9
Subtract 4 from both sides:
x ≤ 5
Therefore, the number must be less than or equal to 5 in order for "a number plus 4" to be at most 9.