This is a question on a diploma i'm about to complete, i've been fine with everything else, but this one really has me stumped. Any help would be appreciated.

The forumla which relates the period of oscillation, T seconds, of a pendulum of length l metres is T = 2π √ l/g where g is acceleration due to gravity.

a) Find the period of oscillation of a pendulum 1.25m long (Take the value of g to be 9.81 ms^-2

b) Rearrange the formula to make l the subject.