Question 916920
An explanation really depends on a good drawn figure.  You'll best have to make one.  Mine  (not convenient to show here) uses a shore arrival point between P and the shore's reference point for the inland, Q.  This is, the arrival point on shore is less than three miles away from P on the shore.


That gives a right triangle.  2 miles MP, x distance along the shore from P; and the expression for this rowing distance is {{{(x^2+4)^2}}}.


The shore reference point being 3 miles away from P, another triangle has sides (3-x) and 1, so the hypotenuse is {{{sqrt((3-x)^2+1)}}}, which is the walking distance.


Uniform Rates for Travel has the rule RT=D for rate time distance.  You have two different distances, each at a different rate of travel.

T=D/R, and having two such time quantities corresponding to each distance, you have a total time function:
{{{highlight(T(x)=(1/2)sqrt(x^2+4)+(1/4)sqrt((3-x)^2+1))}}}


The necessary analysis really must use the drawing, labeling parts and lengths, and identifying the needed Right triangles, and then you could formulate the function for total time.  Difficult to give a drawing here.


This can be a derivative Calculus problem, but you can use your graphing calculator.