filling time of a mold with different gate dimensions

Question

A mold having dimensions 100 x 90x20 (all in mm) is filled with molten metal through a gate with height ‘h’ and C.S area A, the mould filling time is t₁. The height is now quadrupled and the cross sectional area is halved. The corresponding filling time is t₂. The ratio t₂/t₁ is

(a) 1/√2                 (b) 1

(c) √2                    (d) 2