speed of blood flow is 30 cm/s near the heart, but only 20 cm/s at a point 40 cm farther along the arterial pathway.

a. how do you find the velocity for that 40 cm distance?
b. the time it takes the blood to flow 40 cm?

a. The average velocity over the 40 cm distance is 25 cm/s, assuming that is slows down at a constant rate.

b. The time it would take to travel the 40 cm at an average velocity of 25 cm/s would be
t = Distance/Vaverage = 40 / 25 = 1.6 seconds

for problem "a" did you add 30 cm/s and 20 cm/s then divided by 2?? thanks

yes

Yes, that's correct. To find the average velocity over the 40 cm distance, you add the initial velocity (30 cm/s) and the final velocity (20 cm/s), and then divide by 2.