Please could I gain some help with the following question, please don't just supply the answer, I need to be able to work it out, thank you. A heat exchanger is using steam flowing at $4$ kg$/$s and $300$ to heat water flowing at $1\mathrm{.}3$ kg$/$s from $15$ to $80.$ Assuming $$ of water and steam are $4\mathrm{.}187.1.1$ and $1\mathrm{.}996.1.1$ respectively, calculate:

a$)$ The rate of heat transfer.

b$)$ The exiting temperature of the steam.