The answer is 50 percent, question is in the details?

If the employee can assemble 1 unit every two minutes once he has the parts, walking to get the parts takes 4 minutes, for a total of 6 minutes per unit. If you reduce the walking time by half (2minutes) then he starts assembling more, 4 minutes per unit.

Long walk units per hour: 60/6 = 10units per hour

Shorter walk: 60/4 = 15units per hour

change in production = (short walk-long walk)/(long walk) = (15-10)/10 = .5 or 50% increase

First it takes 6 minutes to produce a widget. Second it takes 4 minutes to produce a widget. In one hour he could produce 10 and then 15 so production goes up by 5/10 or 50%.

Originally, the total production time is:

T_0 = t_walking + t_assembly = 4 + 2 = 6 min

And the number of units he produces in time t is:

N_0 = t / T_0 = t / (6 min)

Now, the total production time is:

T = t_walking + t_assembly = 2 + 2 = 4 min

And the number of units he produces in time t is:

N = t / T = t / (4 min)

The percent change in number of units produced is:

% = [(N / N_0) - 1] x 100% = [(T_0 / T) - 1] x 100% = [(6/4) - 1] x 100% = 50%