6. The article “Earthmoving Productivity Estimation Using Linear Regression Techniques” (S. Smith, Journal of Construction Engineering and Management, 1999:133–141) presents the following linear model to predict earthmoving productivity (in m3 moved per hour): Productivity = − 297.877 + 84.787x1 + 36.806x2 + 151.680x3 − 0.081x4 − 110.517x5 − 0.267x6 − 0.016x1 x4 + 0.107x4 x5 + 0.0009448x4 x6 − 0.244x5 x6 where x1 = number of trucks, x2 = number of buckets per load, x3 = bucket volume, in m3 x4 = haul length, in m x5 = match factor (ratio of hauling capacity to loading capacity), x6 = truck travel time, in s

a. If the bucket volume increases by 1 m3 , while other independent variables are unchanged, can you determine the change in the predicted productivity? If so, determine it. If not, state what other information you would need to determine it.

b. If the haul length increases by 1 m, can you determine the change in the predicted productivity? If so, determine it. If not, state what other information you would need to determine it.