Here, `m = + 3` (because image is erect)

`R = -36 cm, u = ? Let u = -x`

As `m = (h_2)/(h_1) = (+ v)/(-u) = 3 :. v = -3 u = 3 x`

As `(1)/(u)+(1)/(v)=(1)/(f)=(2)/( R) :. (1)/(-x)+(1)/(3x)=(2)/(-36)`

`(-3 + 1)/(3x) = - (1)/(18)` or `3x = 36 :. x = 12 cm`

`:. u = -12 cm`.