An object that is accelerating may be a- slowing down b- gaining speed c- changing direction d- all of the above !

All three of those things are forms of "acceleration".

For Blake:

3 boxes at a distance of 10 meters each, each box weighs 20 N

Work done by Blake = 3 * 10m * 20N
                                 = 600 J
Power = 600 J/ 2 min
           = 300 J/min

For Sandra:

4 boxes, 15 N each at a distance of 12 meters each. 

Work done by Sandra = 4 * 15 N *12m
                                    =  720 J
Power = 720 J/ 4 min
           = 180 J/min

Blake does less work than Sandra. 
Blake's power is more than Sandra's.