2.  Initial blood flow is 5 ml/min.  Flow is related to radius of a blood vessel to the Fourth power.  Therefore, doubling the radius results in a 16-fold increase.  If r=1  1 x 1 x 1 x 1 = 1 ;  If  r=2, 2 x 2 x 2 x 2 = 16  If r=4, 4 x 4 x 4 x 4 = 256, for every doubling there is a 16-fold increase.  Therefore,  the new flow rate would be 5 x 16 = 80 ml/min.

3.  Hydrostatic pressure favoring filtration = 34 - 10 = 24 mmHg.  Osmotic pressure favoring reabsorption = 25 -1 = 24 mmHg.  Therefore, no net flow would occur.  The forces are equal and opposite.
 

4.  Flow is proportional to radius to the 4rth power.  At a flow of 1 unit, the radius would equal 1 (the 4rth root of 1).  To reduce flow to 1/2 original rate.  What number raised to the 4rth power equals 1/2 ??    Take the 4rth root of 1/2.  This is 0.84.  Therefore, the new radius would be 0.84.  This is a 16% decrease in radius from a start of 1 or a decrease to 84 % of its original value.