You actually don't have enough information to solve this problem.
The idea here is that when a gas is collected over water, the total pressure of the sample will include the vapor pressure of water at the temperature at which the gas was collected.
SInce no mention of this vapor pressure was made, you will have to either look it up, or calculate it using the Antoine equation. But then again, you'd need to look up the Antoine constants for water, so I'll just use the known value without actually calculating it
Now, according to Dalton's Law of partial pressures, the total pressure of a mixture of gases represents the sum of the partial pressures of each individual component of said mixture.
In your case, this can be written as
#P_"total" = P_"water" + P_"gas"#
This means that the pressure of the gas is equal to
#P_"gas" = P_"total" - P_"water"#
#P_"gas" = "751.5 mmHg" - "25.137 mmHg" = color(green)("726.4 mmHg")#