How would you do these math problems from math0303?

Idk what the problems are called but this is a question.. d varies directly with e and d=98 when e=7. Find d when b=13. There are two more problems e varies inversely with f and e=21 when f=5. Find e when f=11 last problem is a varies jointly with b and c and inversely with c. A=5, b=10, c=3, and d=4. Fina d when b=15, c=4, and d=20.