Kim earns $30 for babysitting on Friday nights. She makes an average of $1.25 in tips per hour. Write the function of Kim's earnings, and solve for how much she would make after 3 hours.
y = 1.25x + 30; $33.75
y = 30x + 1.25; $43.75
y = 30x + 1.25; $91.25
y = 1.25x + 30; $31.25