During the dry season a village get its water from a reservoir after 6 weeks there are 16,800 gallons left in the reservior after 10 weeks there 5,600 gallons left all of the water is used during the dry season. what is the total number of weeks in dry season?

(6,16800),(10,5600)
slope = (5600 - 16800) / (10 - 6) = -11200/4 = -2800

y = mx + b
slope(m) = -2800
use either of ur points...(10,5600)...x = 10 and y = 5600
now we sub into the formula and find b, the y int 
5600 = -2800(10) + b
5600 = -28000 + b
5600 + 28,000 = b
33600 = b

so the equation is : y = -2800x + 33600...with y being the number of gallons and x being the number of weeksand if all of the water is used up in the dry season, then to find the number of weeks, we have to let y = 0

0 = -2800x + 33600
2800x = 33600
x = 33600 / 2800
x = 12 <== the dry season is 12 weeks

38 dollars is your answer.