The mass of a container is 39kg when is 5/6 filled with water. its mass is 29.85kg when it is 5/8 filled with water. what is the mass of the container when it is empty?

(5/6,39),(5/8,29.85) 
slope = (29.85 - 39) / (5/8 - 5/6) = - 9.15 / (-5/24) = -9.15 * - 24/5 = 
219.6 /5 = 43.92

y = mx + b
slope(m) = 43.92
(5/6,39)x = 5/6 and y = 39
now sub and find b, the y int
39 = 43.92(5/6) + b
39 = 36.6 + b
39 - 36.6 = b
2.4 = b

so ur equation would be : y = 43.92x + 2.4

and when it is empty, x = 0
y = 43.92(0) + 2.4
y = 2.4 <=== so when the tank is empty, the mass is 2.4 kg