Answer: The required constant of proportionality is 10.
Step-by-step explanation: Given that y is directly proportional to x, and y = 150 when x = 15.
We are to find the constant of proportionality.
According to the given information, we can write
![y\propto x\\\\\Rightarrow y=kx~~~~~~~~~~~~~~~~[\textup{where k is the constsnt of propotionality}].](https://img.qammunity.org/2020/formulas/mathematics/middle-school/l32d2ibgjg48uaeonpg04n5bxh1a9bfpg1.png)
When y = 150 and x = 15, we get from the above equation that

Thus, the required constant of proportionality is 10.