4a. 2L + 10C = 2000
2L - 2L + 10C = -2L + 2000
10C = -2L + 2000
10 10
C = -0.5L + 200
4b. 2L + 10C = 2000
2L + 10C - 10C = -10C + 2000
2L = -10C + 2000
2 2
L = -5C + 1000
The variable L is a linear function of C because it shows that it can be changed into slope - intercept form in order to find the values of the two variables.