Pressure at the place remains the same for both water and mercury.
Pressure exerted by mercury = density of mercury * height of mercury column * g (acc. due to gravity)
=> Pressure exerted by mercury = 13.6 * 76 * g
=> Pressure exerted by mercury = 1033.6 g
Pressure exerted by water = density of water * height of water column * g (acc. due to gravity)
=> Pressure exerted by water = 1 * h *g
=> Pressure exerted by water = h g.
Now, According to question,
1033.6 * g = h* g
=> h = 1033.6 cm.
Therefore, the height of water column which will exert on its base the same pressure as the 76 cm column of mercury is 1033.6 cm..