Answer:
16)
.......as required
18)
..........as required
Explanation:
16)

Multiply both the side by 'a' and divide both the side by 'u'

Cancel 'u'on Left side and 'a' on right side we get
.......as required
18)
.......Given
Dividing by 4 on both the side we get

Cancel 4 on right side we get
..........as required