So this is an assigned problem, but I can assure you that I have tried this problem multiple times and still seem to get the incorrect answer.

If we suppose the unknown rate of change in the angle as z...

x/8 = tan z

x = 8 tan z

dx/dt = 8 sec(z)^2 * dz/dt

dz/dt = 1/8 cos(z)^2 * dx/dt

dz/dt = 1/8 cos(z)^2 * 1.3

dz/dt = 1.3/8 cos(z)^2

dz/dt = 1.3/8 (8/10)^2 <-- cos(z) is 8/10

dz/dt = 1.3/8 (64/100)

dz/dt = 0.104 rad/s

But it still says I'm wrong...? I've done the problem from the beginning a few times, and I still get the same answer. HELP!