In a field of ducks and a dog someone counted 25 heads and 80 legs. how many dogs and ducks are there

Ducks have two legs while dogs have four legs and their are 25 heads, so there must be 15 dogs and 10 ducks.
15(heads) x 4(legs/head) = 60 legs      10 (heads) x 2 (legs/head) = 20 legs
                                      60 legs + 20 legs = 80 legs
                                      15 heads + 10 heads = 25 heads
(legs/head) is read as legs per head

The answer is "a"radius = 12.7 unitsdiameter = radius × 212.7 units × 2 = 25.4 units