Polyethylene can be produced from calcium carbide according to the following sequence of reactions

The mass of polyethylene which can be produced from 40.0 kg of ${\mathrm{CaC}}_2$ is

64 grams ${\mathrm{CaC}}_2$ gives 26 grams $HC\equiv CH$

So 64 kg ${\mathrm{CaC}}_2$ gives 26 kg HC$\equiv$CH

So 40 kg ${\mathrm{CaC}}_2$ gives 26 x 40/64 kg $\mathrm{HC}\equiv \mathrm{CH}$

                                       = 16.25 kg $\mathrm{HC}\equiv \mathrm{CH}$

Now 26 kg $\mathrm{HC}\equiv \mathrm{CH}$ gives 28 kg polythene

So 16.25 kg $\mathrm{HC}\equiv \mathrm{CH}$ gives 28 x 16.25/26 kg polythene

                                = 17.5 kg