#### Answer

a. $15$
b. $0$

#### Work Step by Step

$$n=dq+r=d(n\ div\ d)+n\ mod\ d$$
$$30=2(30\ div\ 2)+30\ mod\ 2=2(15)+0$$
The numbers $n\ div\ d$ and $n\ mod\ d$ are defined to be the numbers $q$ and $r$, respectively, as given in the quotient-remainder theorem. See page 181 of the text.