This problem can be solve with the simple rule of three:
[tex]\begin{gathered} 1\text{ fortnight}\to21\text{hours of practice} \\ 7\text{ weeks}\to x \\ x=\frac{7weeks\cdot21\text{ hours of practice}}{1fortnight} \\ 7\text{ we}eks=7\cdot7days=49days \\ 1\text{ fortnight=15days} \\ x=\frac{49days\cdot21\text{ hours of practice}}{15\text{ days}}=68.6\text{ hours of practice} \end{gathered}[/tex]In 7 weeks Ed practice 68.6 hours.
Note we convert week and fortnight to days.
