Tolong dong no 16, makasih:)

Fa/Aa = Fb/Ab
rumus luas lingkrang dgn diaeter = 1/4 x pi x d²
20/(1/4 x pi x d²) = Fb/(1/4 x pi x d² x 4)
20/(1/4 x pi x d²) = Fb/(pi x d²)  
--> pi x d² masing2 ruas dicoret
20/(1/4) = Fb/1
kali silang
1/4Fb = 20
Fb = 20 x 4
= 80 N

B