Pressure

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I thought total pressure = atmospheric pressure + (height x density x 9.81) but how comes in the solution to the above question they just worked out (height x density x 9.81) ?

I was doing a question about an air bubble under water earlier and I used
total pressure = atmospheric pressure + (height x density x 9.81) and got the answer right. How comes we don't use it here?

It asks for the pressure difference, not for the pressure at the bottom.
Pressure at bottom = density*h*g + p0 (p0=atmospheric pressure)
Pressure at top = p0
Difference between the two = density*h*g

Why is the pressure at the bottom (density*h*g) whereas the pressure at the top is (p0) ?

Thanks

It isn't. The exercise says: 'Calculate the pressure difference'.
pressure difference = pressure at bottom - pressure at the top = density*h*g + p0 - p0 = density*h*g

So the pressure at the bottom = density*h*g + p0
and pressure at the top = p0

My question is why does the formula for the respective pressures differ?