How do you write an equation for this?

Y = -3/1.5x + 3 or y = -2x + 3. we can assume that the points the line passes through are (0, 3) and (1.5, 0). Thus, using rise over run, we can figure out that the slope is -3/1.5 which reduces to -2. The y intercept (where the line meets the y axis) is 3, so we add that at the end.