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

(1) Area of a square: A=s^{2}

A is proportional to s.

(2) Average speed: r=d/t

R is proportional to t.

(3) Surface area of a cube: S=6r^{2}

S is proportional to r.

(4) Free vibrations:

is proportional to W.