Mr. harris has some money in his wallet. he pays the babysitter $12 an hour for 4 hours of babysitting. his wife gives him $10, and he puts the money in his wallet. by how much does the amount in his wallet change? ?

Ok. So since we do not know the total he starts with, we can use a variable.

x is his first amount.

Then he pays the babysitter 12 dollars an hr for 4 hours.

12*4 = 48

so x-48

x-48

Now, his wife gives him $10

-48+10 = -38

The amount in his wallet changes by -38. Therefore, he loses 38 dollars. 

How much went out ?

(12 x 4) = $48.

How much went in ?

$10 .

The change = 48 out + 10 in = 38 less.