The answer is 43.95 in ≈ 44 in
Step 1. Sum up their wingspans which will reflect the perimeter of the tree they wrap.
Step 2. From the calculated perimeter in step 1, find the diameter.
Step 1.
Perimeter of the tree is the sum of their wingspans:
P = 5'6'' + 6'
5'6'' = 5 * 12 in + 6 in = 66 in
6' = 6 * 12 in = 72 in
P = 66 in + 72 in = 138 in
Step 2.
Perimeter of a circle with radius r is:
P = 2 r π
Since diameter is twice of radius (d = 2r), then
P = d * π
P = 138 in
π = 3.14
138 in = d * 3.14
d = 138 in / 3.14
d = 43.95 in ≈ 44 in