#### Answer

Estimate: 17
Exact: $17\frac{1}{6}$

#### Work Step by Step

To estimate, we round the fractions to the nearest whole number:
Estimate=$22-5=17$
Next, we find the exact answer:
Exact=$21\frac{6}{6}-4\frac{5}{6}=(21-4)+(\frac{6}{6}-\frac{5}{6})=(17)+(\frac{1}{6})=17\frac{1}{6}$
Which is close to the estimate.