Answer: The mystery length is 12
Explanation:
We know that the left side of the triangle measures a total of 65 units and that the first part of the triangle measures 52 units. This leaves the second part of the lefft side having to equal to 13 because 65 - 52 = 13. We can use a ratio of the two triangle lengths to make a pattern that is shown as 13 : 52, with 13 being the length of the side of the smaller triangle. the ratio 13 : 52 can be shortened to 1 : 4. We know in the right side of the triangle that the larger triangle measures 60 units. Now apply it to the ratio: ? : 60. The question mark's value must be 25% of the larger length so the mystery length is 12.