Answer:
In the graph we can find two points, lets select:
(2, 15) and (4, 30)
Those are the first two points.
Now, for two pairs (x1, y1) (x2, y2)
The slope of the linear equation y = s*x + b that passes trough those points is:
s = (y2 - y1)/(x2 - x1)
So the slope for our equation is
s = (30 - 15)/(4 - 2) = 15/2
then our linear equation is
y = (15/2)*x + b
now we can find b by imposing that when x = 2, y must be 15 (for the first point we selected)
15 = (15/2)*2 + b = 15 + b
b = 15 - 15 = 0
then our equation is:
y = (15/2)*x
Where we used a division and a multiplication.
 
        
             
        
        
        
Write as a function equation: where f(x) is the same as "y"
f(x) = 5 + 1x   ------  y = 1x + 5
Use:  y = mx + b  (Where m = slope and b is y intercept)
Slope is 1 and y intercept is +5 
Remember slope is rise over run so 1 can be written as 1 / 1 and interpreted as rise 1 and run 1 both in the positive direction. 
        
                    
             
        
        
        
That what the answer is because on what is asking the answer is gonna be 6,1761
        
             
        
        
        
Answer:
Let the current speed be "c";
Then the boat speed in still wate is "5c":
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Upstream speed:
distance = 12 miles ; rate = 5c-c = 4c mph ; time = 12/4c = 3/c hrs
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Downstream speed:
distance = 12 miles ; rate = 5c+c = 6c mph ; time = 12/6c = 2/c hrs
Step-by-step explanation:
Equation:
time + time = 2 1/2 hrs
3/c + 2/c = 5/2
Multiply thru by 2c to get:
6 + 4 = 5c
c = 2 mph (speed of the current)
5c = 10 mph (speed of the boat in still water)
 
        
             
        
        
        
3/4 + 3/4 = (3 + 3)/4 = 6/4 = 3/2