Process engineering question about pressure

A question states: Two mercury manometers, one an open end and the other a sealed (or closed) end, are attached to an air duct. The reading on the open-end manometer is 30mm and that on the sealed end is 780mm. Determine the absolute pressure in the duct, the gauge pressure in the duct, and the atmospheric pressure. Give answers in Pa.

What I know:
Absolute pressure = gauge pressure + atmospheric pressure
Gauge pressure = absolute pressure - atmospheric pressure
How to convert (mm Hg) into Pa

What I don't know: how to implement the pressure rules (which reading is what).

Please show all working and explain as easily as possible.
Thanks in advance

The open end manometer is reading gauge pressure and the closed end one is reading absolute. You have to do the simple math to get atmospheric pressure.

the absolute pressure can never be negative. So you need to get a positive answer. It has to be related to 780mm-30mm = 750mm as otherwise, the result is negative. Simple logic Eh?