For this question you use the Pythagorean Theorem, with the equation A^2 + B^2 = C^2, for this problem the best way to solve it would be to draw a rectangle and label the shorter sides 3.7, longer sides 4.7, and to draw a diagonal line through the center.
To solve the equation you only need to find the hypotenuses (the longest side of the triangle) of one triangles since the triangles have the same measurements.
For your equation A^2 + B^2 = C^2, the a and the b represent the two shorter sides and the c represents the hypotenuse, after plugging in your number you get this equation,
3.7^2 + 4.7^2 = c^2, you then proceed to work out this equation by squaring the two numbers, you now have, 13.69 + 22.09 = c^2, you then add those two numbers and get, 35.78 = c^2, you now have to isolate the c to find the hypotenuse, to do this you find the square root of both sides, your result is c = 5.98, you then add 5.98, 3.7, and 4.7 to find the perimeter, which is 14.38, this is the perimeter of both of the triangles.