Use (t1,y1)=(0,109.5) and (t2,y2)=(15,377.9) to find the slope:

\(\displaystyle{m}=\frac{{{y}{2}-{y}{1}}}{{{t}{2}-{t}{1}}}=\frac{{{377.9}-{109.5}}}{{{15}-{0}}}\sim{17.9}\)

Since the y-intercept is the y-value, when t=0, we know that b=109.5 from the first point. So, the equation is: y=17.9t+109.5