Answer:
40 (cm)
Explanation:
0. make up a new picture with additional elements (radius of the inscribed circle, it's 'x'; and some elements as shown in the attached picture);
1. the formula of the required perimeter is P=a+b+c, where c- hypotenuse.
2. apply the Pythagorean theorem: a²+b²=c², where c - hypotenuse, then calculate value of 'x' (attention! x>0, the length is positive value !)
3. substitute 'x' into the formula of the required perimeter. The result is 40.
PS. All the details are in the attached picture, answer is marked with red colour.