imc

Converting feet to yards and minutes to second, we see that the truck travels $\frac{b}{18}$ yards every $t$ seconds for $180$ seconds. We see that he does $\frac{180}{t}$ cycles of $\frac{b}{18}$ yards. Multiplying, we get $\frac{180b}{18t}$, or $\frac{10b}{t}$, or $\boxed{\frac{10b}{t}}$.