Answer: second option
Explanation:
You know that it is a right triangular window frame.
Then, you can use the Pythagoren Theorem to find the lenght of the third side:
![a^2=b^2+c^2](https://img.qammunity.org/2020/formulas/mathematics/middle-school/g7lqyavlhxie81evds9kmmjv6zlmpg9yqr.png)
Where "a" is the hypotenuse (or the longest side), and "b" and "c" are the legs .
Then, you can solve for one of the legs:
![b^2=a^2-c^2\\b=√(a^2-c^2)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/5ni3emvalfzi0xfofm2ttfxt1relobc6fi.png)
Since you know the lenght of the hypotenuse and the lenght of one leg, you can substitute values.
Therefore, you get:
![b=√((87in)2^-(63in)^2)\\b= 60in](https://img.qammunity.org/2020/formulas/mathematics/middle-school/h7xr0ge8swk14kp3zcf7vz80c8t4t4es75.png)