To solve this problem, we must first assume that the two gases acetylene and oxygen to act like an ideal gas so that we can use the ideal gas equation:
P V = n R T
where,
P is the pressure inside the tank, V is the volume of the tank, n is the number of moles of gas, R is the universal gas constant and T is the absolute temperature
Now to ensure that we run out of each gas at the same time, we must also assume that n and T are equal for both gases, therefore:
P V = constant
So now we can equate the PV for the two gases to find for the pressure of the other tank:
145 atm (5.50 L) = P (4.00 L)
P = 199.375 atm