A scientist created a scatter plot to represent the heights of four plants over time. Then, she found a line of best-fit to model the height in centimeters of each plant after x days. The equations of each trend line are given in the table.

Trend Line Equations
Plant Equation of trend line
1 y = three-halves x + three-halves
2 y = 2 x + 1
3 y = one-half x + 3
4 y = three-halves x + 1

According to the trend line equations, which plants are growing at the same rate per day?
1 and 2
1 and 4
2 and 3
2 and 4