Chemistry question..please help.?

This question is for a pre lab ignment that we have to do. A sample of helium is collected by displacing 145 mL of water. the pressures of the gas and the atmosphere are equalized using the method described in this experiment. The atmospheric pressure is 745 mmHg. The temperature of the water and that of the gas are identical at 26 degrees C. How many moles of helium have been evolved?