**1. The problem statement, all variables and given/known data**
The velocity v of blood that flows in a blood vessel with radius R and length l at a distance r from the central axis is v(r), where P is the pressure difference between the ends of the vessel and η is the viscosity of the blood.

**(a)**Find the average velocity v_ave (with respect to r) over the interval 0 ≤ r ≤ R.

**(b)**Compare the average velocity v_ave with the maximum velocity v_max.(v_ave/v_max)

So I need to set the problem up, into an integral form, to find the avg velocity for part A. The integration limits for the integral should be from zero to Big R, multiplied by (1 over big R) to get our average value. Now the problem is, every thing in the equation except the (1/4) is a variable. How would I even begin to integrate this?

Thanks.