Question

A gas mixture with a total pressure of 750 mmHg contains each of the following gases at the indicated partial pressures: , 265 mmHg; Ar 134 mmHg; and ,O2 157 mmHg; The mixture also contains helium gas.

Answer 1

You have two problems. The first is you didn't identify the gas with 265 mm Hg pressure. The second is you didn't ask a question. I will assume the 265 mm Hg gas is just X and I will assume the question is, "What is the pressure of He."
Ptotal = PX + PAr + PO2 + PHe.
Substitute and solve for PHe.

Answer 2

189 he?