Explanation:
the simplest approach is a linear equation (a line), since we only got 2 data points.
and as we know, any set of 2 points creates a line.
so
y = ax + b
due to y = 0 for x = -2
0 = -2a + b
2a = b
and from
y = -25 for x = 8 (and the first equation) we get
-25 = 8a + 2a = 10a
a = -25/10 = -2.5
our equation is
y = -2.5x + 2(-2.5) = -2.5x - 5