Hello Juan -
Not sure what level of math you are working with, as this can be solved in a number of different ways. Also, though you don't exactly mention it, I am assuming point A is the place on the shore where the nearest point to C is. We need to find AP, the distance from that to the place where we land.
So let's try something. Suppose AP = 1. How long would that take? the hypotenuse of the triangle ACP (given AP is 1) would be the square root of 4^2 plus 1^2, or about 4.12 miles. At 3 mi/hr, it would take 1.37 hours. Now we walk 6 miles (7-1) at 4 mi/hr, so that takes 1.5 hours. So the total time would be, given AP =1, 2.87 hours. We wanted 2.67 hours, so it is a little high.
So, should we make AP larger or smaller to get the time to be shorter? By how much? Try a few other distances. Or can you graph this on a calculator and see what the result will be? The equation can easily be written by setting the distance AP = x, and then:
time = (row dist)/3 + (walk dist)/4
walk distance would be 7-x, row distance would be square root of x^2 + 4^2
If this was a problem in a calculus class, it can be solved analytically by setting up a minimum condition. Since the problem appears to be tagged as "algebra", the above method would give results. Without doing any further work, we can estimate the answer. Make a guess. Larger than one, or smaller?
Hopes this helps you finish the problem. (The simple way is try whole numbers, which will work here. You might especially try x = 3, but the calculator will tell you the same story if you graph the quadratic.)
Ken