Sid has a job at Morgan Motors. The salary is $1200 a month, plus 3% of the sales price of every car or truck Sid sells (this is called a commission). (a) The total of the sales prices of all the vehicles Sid sold during the first month on the job was $72000. What was Sid's income (salary plus commission) ? (b) In order to make $6000 in a single month, how much selling must Sid do? (c) Write a linear equation that expresses Sid's monthly income y in terms of the value x of the vehicles Sid sold. (d) Graph this equation. What is the meaning of its y-intercept, and the meaning of its slope?