Given:
- Atmospheric pressure = 76 cm of mercury
- Density of mercury = 13600 kg/m^3
- Pressure at a depth of water = 2 atmospheres

To find:
- Depth of water at which the pressure is equal to 2 atmospheres

Formula:
- Pressure in a fluid = ρgh (where ρ is the density of the fluid, g is the acceleration due to gravity, and h is the depth)

Steps to calculate the depth of water:

Step 1: Convert atmospheric pressure from cm of mercury to Pascals (SI unit of pressure).
- 1 atmosphere = 101325 Pascals
- Given atmospheric pressure = 76 cm of mercury
- Conversion factor: 1 cm of mercury = 1333.22 Pascals (approximately)

Therefore, atmospheric pressure = 76 cm of mercury * 1333.22 Pascals/cm of mercury = 101325 Pascals

Step 2: Calculate the pressure at a depth of water equal to 2 atmospheres.
- Given pressure = 2 atmospheres = 2 * 101325 Pascals = 202650 Pascals

Step 3: Determine the depth of water using the formula.
- Pressure in water = ρgh
- Density of water = 1000 kg/m^3 (approximately)

Substituting the values, we have:
202650 Pascals = 1000 kg/m^3 * 9.8 m/s^2 * h

Simplifying the equation, we get:
202650 = 9800h

Step 4: Solve for h (the depth of water).
h = 202650 / 9800
h ≈ 20.67 meters

Therefore, the depth of water at which the pressure is equal to 2 atmospheres is approximately 20.67 meters.

Summary:
The pressure at a depth of water equal to 2 atmospheres is calculated by converting the atmospheric pressure from cm of mercury to Pascals. Then, using the formula for pressure in a fluid, we can determine the depth of water. In this case, the depth is found to be approximately 20.67 meters.