You have two points, the starting point (0, 1, 000,000) and the end point (25, 600,000)
Find the slope, which id the difference in Y over the difference in x:
m = (600,000 - 1,000,000) / (25-0)
= -400,000 / 25
= -16,000
Now you have V -1,000,000 = -16,000(x-0)
Rewrite in terms of V(t):
V(t) = -16,000t + 1,000,000
Now replace t with the years and solve:
1 year = V(1) = -16000(1) + 1,000,000 = -16,000 + 1,000,000 = $984,000
2 years = V(2) = -16,000(2) + 1,000,000 = -32,000 + 1,000,000 = $968,000
20 years = V(20) = -16,000(20) + 1,000,000 = -320,000 + 1,000,000 = $680,000