A wise man once said, "400 reduced by 3 times my age is 133." what is his age?

Let the age of the wise man be x years. And in the question it is said that, 400 reduced by 3 times my age is 133, that is,

400-3x = 133

Now we need to solve for x, and for that first we subtract 133 to both sides

400-133-3x=0

267-3x = 0

3x=267

Next is to get rid of 3 by dividing both sides by 3, that is

x = 89 years

And that's his age.

400-3x=133

-3x=-267

x=89 (his age)