Answer
a) $78\;\rm J$
b) $1.3\;\rm W$
Work Step by Step
a) We know that the prssure is given by
$$P=\dfrac{F}{A}\tag 1$$
where $F$ is the force and $A$ is the area which, in our case, is the cross-sectional area of a tube.
We also know that the work is given by
$$W=FL$$
where $L$ here is the length of the tube.
Hence,
$$F=\dfrac{W}{L}$$
Plugging into (1);
$$P=\dfrac{W}{AL}$$
Now we know that $L$ is the length of the tube (which is the circular system) and is $A$ its cross-sectional area; where its volume is given by $V=AL$.
Thus,
$$P=\dfrac{W}{V}$$
Hence, the work done by the heart is given by
$$W=PV$$
Plugging the known;
$$W=1.3\times 10^4\times 6\times 10^{-3}$$
$$W=\color{red}{\bf 78}\;\rm J$$
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b) We know that the power output is given by
$$P=\dfrac{W}{\Delta t}$$
where $P$ here is power not the pressure.
Thus, the power output during one minute is
$$P=\dfrac{78}{60}$$
$$P=\color{red}{\bf 1.3}\;\rm W$$
