Finding the mole fraction
As you said, the molar percentage is just the molar fraction multiplied by 100. As to the L and V above the molar fractions, they refer to the molar fraction of the component in the liquid and vapor phase, respectively. They are needed since (in general) the molar fraction of a component in a mixture are different in the liquid and vapor phase.

So, from the data in your problem, you know that the molar fraction of carbon disulfide in the gas phase is 0.855, and let's call it $x_{CS_2}^V$. The total pressure is P=263 torr, and since the vapor exhibits ideal behavior, the partial pressure of CS2 is: $P_{CS_2} =x_{CS_2}^V P$. Using Raoult's law (since the liquid exhibits ideal behavior), this partial pressure must be equal to the molar fraction of CS2 in the liquid times the vapor pressure of pure CS2: $P_{CS_2} =x_{CS_2}^L P_{CS_2}^o$. And I am sure you can follow from here.