An independent mail delivery service wants to study factors that affect the daily gas usage of its delivery trucks. using data collected from different trucks on various days, a company analyst uses a software to fit a regression model of the form:

ŷ=49.2+6.1x1-2.6x2+4x3+0.03x4

where
y= volume of gasoline used (in gallons)
x1= weight of truck (in tons)
x2= tire pressure (in psi, pounds per square inch)
x3 =weight of initial package load (in hundreds of pounds)
x4= total distance driven while delivering packages (in miles)

answer the following questions for the interpretation of the coefficient of x, in this model.
a. holding the other vartables fixed, what is the average change in dally fuel used for each additional hundred pounds of package weight?
b. is this change an increase or a decrease?