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Efficiency = 40%

\eta= \frac{work\ done}{heat\ supplied}\\ \\ \Rightarrow 0.4= \frac{20\ kJ}{Heat\ supplied} \\ \\ \Rightarrow Heat\ Supplied= \frac{20}{0.4} =50\ kJ

1\ calorie = 4.184\ J\\50 kJ =  \frac{50}{4.184}\ kcal=11.95\ kcal

So 11.95 kcal heat should be supplied.

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you are ri8 bt my prblm is that i dont know anything abut efficiency so how did you find 0.4 can u plz explain me
40% means 40/100 which is 0.4.
the only physics involved is "the formula of efficiency"
rest is mathematics.