tlong ohh pliisssssssssssss

F = 20 N
x = 0.04 cm = 4 x 10^-4 m

cari dulu konstanta pegasnya
k = F / x = 20 / (4 x 10^-4)
k = 5 x 10^4 N/m

maka e.potensialnya
E.p = ½ k x² = ½ 5 x 10^4 x (4x 10^-4)²
e.p = 4 x 10^-3 joule