ANSWER:
5.82 m/s²
Explanation:
In order to solve the question we make a free body diagram of the situation, like this:
We make the vertical and horizontal force balances, just like this:

With these balances we can calculate the value of the acceleration, like this:
![\begin{gathered} \text{ Given:} \\ \\ F=\mu N\leftarrow F=\mu(mg\cdot\cos43\degree) \\ \\ \text{ We replacing} \\ \\ mg\sin(43)\operatorname{\degree}-\mu(mg\cdot\cos43\degree)=ma \\ \\ g\sin43\degree-\mu g\cdot\cos43\degree=a \\ \\ a=g(\sin43\degree-\mu\cos43\degree) \\ \\ \text{ We substitute each value to determine the acceleration:} \\ \\ a=9.8(0.682-0.12\cdot0.731) \\ \\ a=5.82\text{ m/s}^2 \end{gathered}]()
The acceleration of the boat and riders is 5.82 m/s²