a)
[tex] \frac{4}{5} x = 80[/tex]
[tex]x = 80 \times \frac{5}{4} = 20 \times 5 = 100[/tex]
b)
[tex]1 \frac{1}{3} x = 4 \frac{1}{9} [/tex]
[tex] \frac{4}{3} x = \frac{37}{9} [/tex]
[tex]x = \frac{37}{9} \times \frac{3}{4} = \frac{37}{12} = 3 \frac{1}{12} [/tex]
