Let's start by translating the sentence into an equation.
Let the number be represented by "x".
"Ten less than 40% of a number" can be expressed as:
0.4x - 10
"Is" means equals, so we can write:
0.4x - 10 = -4
Now we can solve for x:
0.4x = 6
x = 15
Therefore, the number is 15.