The difference between 10 and three times a number is 31.

10 - 3h = 31

minus both sides by 10 to get:

-3h = 21

divide both sides by - 3 is:

h = - 7

Let's write an equation describing this relationship:

let's call the number (n)

10 - 3n = 31

now we solve for 31

subtract 10 on both sides

10 - 3n - 10 = 31 - 10

-3n = 21

now divide by 3 on both sides

and we get

n = - 7