`a) -19 + 7 + 9 + 19`
`= (-19 + 19) + (7 + 9)`
`= 0 + 16`
`= 16`
$\text { b) $\frac{2}{7}$ . 5$\frac{1}{4}$ - $\frac{2}{7}$ . 3$\frac{1}{4}$ }$
$\text { = $\frac{2}{7}$ . ( 5$\frac{1}{4}$ - 3$\frac{1}{4}$ ) }$
$\text { = $\frac{2}{7}$ . [ ( 5 + $\frac{1}{4}$ ) - ( 3 + $\frac{1}{4}$ ) ] }$
$\text { = $\frac{2}{7}$ . ( 5 + $\frac{1}{4}$ - 3 - $\frac{1}{4}$ ) }$
`= 2/7 . ( 5 - 3 )`
`= 2/7 . 2`
`= 4/7`
