This is how you do the practise 2.2 question 14 in the textbook.

The question:Saida owns 125 shares of an oil company. One day, the value of each share dropped by 31 cents. The next day the value of each share rose by 18 cents. What was the cahnge in the value of Saida's shares?

The solution : Lets say each share is a dollar. now it drops by 31 cents. Its value is now 69 cents. Now we add 18 cents. We have 87 cents. Then we have to figure out what the value change would be now for one share. A share has dropped by 13 cents. Times 13 by 125, or you can do it a simpler way by times by 5 first to get 65 cents . Times by 5 again to get $3.25. Times by 5 one more time to get the final answer $16.25.
The Answer :The total value change of Saida's shares altogether dropped by $16.25.