change in speed and productivity with change in feed and depth of cut

Question

A generalized tool if equation for carbide tool for machining steel is given by VT^aF^bD^c = K,

Where V = Cutting speed, meters/min

T = Tool life, minutes

F = feed, mm/rev

D = depth of cut in mm, Indices have magnitudes a=0, b=0.3, c=0.15 

i) If the feed is halved and depth of cut doubled, for identical tool life of 60 minutes, the percentage change in speed

(a) 5%                    (b) 11%

(c) 25%                  (d) 130%

ii) the change in productivity for the new processing conditions

(a) 5%                    (b) 11%

(c) 25%                  (d) 130%