The partial pressure of each gas in a mixture is proportional to its mole fraction.
n = m / M
M (CO) = 28 g/mol
M (CO2) = 44 g/mol
M (CH4) = 16.04 g/mol
n (CO) = 4 / 28 = 0.14 mol
n (CO2) = 11 / 44 = 0.25 mol
n (CH4) = 2 / 16.04 = 0.13 mol
Sum of n = 0.14 + 0.25 + 0.13 = 0.52 moles
CO mole fraction = 0.14 / 0.52 = 0.27
CO2 mole fraction = 0.25 / 0.52 = 0.48
CH4 mole fraction = 0.13 / 0.52 = 0.25