The original quantity is 10 and the new quantity is 13. What is the precent change? Is it an increase or decrease?

Ibelieve it would be letter c (:

So don't take my word i'm not exactly a mathematical person but i would assume a. because while selling the soap every month you increase in sells so you would by 11 percent. the you would get the factor 0.89 which if i had to guess would be the monthly profit over 11 probably wrong tho