To find the y-intercept, simply look at the constant at the end of this equation. Let's look at the linear function equation. The equation is y=mx+b. In this case, the constant is b. The constant always is the non-x term, so for the question, the y-intercept would be -11.
After 1 sec it would be 65 m/s after 2 sec it would be 55 m/s after 3 sec it would be 40 m/s after 4 sec it would be 20 m/s and so on. The equation for this is S = 70 - (-5(t)) where s=speed and t=time passed
