Final answer:
The value of the missing side is 300.
Step-by-step explanation:
To find the value of the missing side, you need to set up a proportion using the given information. Let's assume the missing side is represented by x. The ratio of the given side to the missing side can be written as 15/x = 1/20. To solve for x, cross-multiply and solve the resulting equation. 15/x = 1/20 can be rewritten as 15 * 20 = x. Therefore, x = 300. The value of the missing side is 300.