Answer:
They are all positive because you must go right.
They are all negative because you must go down.
Step-by-step explanation:
Example. (1,-4)
You go over one.
Down 4
Answer:

Step-by-step explanation:
For this case we have two points given (-1,6) and (1,5)
And we want to complete the point slope equation of the line:

We need to find the slope and we can use the following formula:

And replacing the info we got:

And then the equation would be given by:

And our final answer would be:

Let the speed of the current equal c
and the speed of the boat in still water equal b.
b + c = 1.5 (b - c)
b + c = 1.5b - 1.5c
0.5b = 2.5c
b = 5c
The speed of the current is 1.5 mph so
b = 5 * 1.5 = 7.5 mph