Pls help ASAP I DONT have time

The graph represents the gallons of water in a water tank with respect to the number of hours since it was completely filled

How do you determine whether a relationship represented as as graph is linear or nonlinear

1) in triangle the, what is the measure of angle t (in degrees)? 2) in triangle bat, the measure of angle b is 66∘, and the measure of angle t is 77∘.what is the measure of the exterior angle at a (in degrees)?