Fill in the blank with either “directly” or “inversely”.

(1) Area of an equilateral triangle: A=(√3s^{2})/4

A is proportional to s.

(2) Average speed: r=d/t

R is proportional to t.

(3) Surface area of a sphere: S=4πr^{2}

S is proportional to r.

(4) Free vibrations:

is proportional to W.