Answer:
coefficients are the number attached to the variables :75d+8w+25
75 , 8 and the constant is 25. the variables are d and w
if he works for 5 days(d) and installed 48 windows(w)
75 d + 8 w+25
75(5)+8(48)+25= 784 dollars
if Javier get increase of 40 dollars for snack, only the constant change, because the coefficient depends on work days and the number of windows installed, and since only the increase in his stipend, therefor the increase will be the constant value only.