An adiabatic heat exchanger is used to heat cold water at $$15^\circ C$$ entering at a rate of 5 kg/s by hotair at $$90^\circ C$$ entering also at rate of 5 kg/s. If the exit temperatureof hot air is $$20^\circ C$$, the exit temperature of cold water is

A

$$27^\circ C$$

B

$$32^\circ C$$

C

$$85^\circ C$$

D

$$90^\circ C$$