Answer:
d = 17.5499287748 inches or 17.5 inches to 1 decimal place
Explanation:
find the diagonal line passing through the middle of the bottom rectangle:
a² + b² = c²
10² + 8² = c²
100 + 64 = 164
c² = 164
c = √164
c = 12.8062484729
find d:
a² + b² = c²
12² + 12.80624847298² = c²
144+ 164 = 308
c² = 308
c = √308
c = 17.5499287748
therefore d = 17.5499287748 inches or 17.5 inches to 1 decimal place