Jeffrey multiplies a number by itself and then adds 10. his answer is 23.69. what is the number?

To find the answer just do the opposite-
If you added 10, then you subtract 10.
So 23.69 - 10 = 13.69
If you multiply an number by itself, you are basically doing exponents so do the opposite of exponents which is root square.
So you root square 13.69 
Which equals 3.7 
So the number is 3.7