31)
a) Mobile plan A: y = 21.4x + 10
Mobile plan B: y = 18.5x + 14
b) Substitute 100 for "x" into each equation:
Plan A: y = 21.4(100) + 10
= 2140 + 10
= $2150
Plan B: y = 18.5(100) + 14
= 1850 + 14
= $1864
Therefore, you should pick Mobile Plan B because it costs less.
