Proportionality constant can be defined as ratio, so its fraction.
To the numerator we can put 1.5 (orange) and to the denominator we can put 1 (apple). Then we will obtain proportionality constant. We have to simplify it finally.
reminder. 1.5=+[tex] \frac{3}{2} [/tex]
[tex] \frac{ \frac{3}{2} }{1} = \frac{3}{2} [/tex] - its the result