Nothing "weighs" 56.7 grams. "Gram" is a unit of mass, not force or weight.
On Earth, 28.35 grams of mass weigh about 1 ounce .
1 dozen of anything = 12 of them
If each tennis ball has 56.7 grams of mass, then a dozen of them
have
(12) x (56.7) = 680.4 grams of mass .
Their weight is (680.4 grams) x (1 ounce / 28.35 grams) =
(680.4 / 28.35) = 24 ounces.
That's 1.5 pounds.
