Does anyone know how to solve this?

14.76

Step-by-step explanation:

First find the length of the diagonal across the bottom using the Pythagorean theorem

a^2 + b^2 = c^2 where a and b are the legs and c is the hypotenuse

12^2+5^2 = c^2

144+25 = c^2

169 = c^2

Take the square root of each side

sqrt(169) = sqrt(c^2)

13 = c

Then find the length of the diagonal across the  middle using the Pythagorean theorem

7^2 + c^2 = d^2

7^2 + 13^2 = d^2

49+ 169 = d^2

218 = d^2

Take the square root of each side

sqrt(218) = sqrt(d^2)

14.76482306 = d

To the nearest thousandth

14.76

picture below