A4. In the forest, there are 80 trees planted. Forester Matic marks every third tree, and Forester Jure marks every fifth tree. They will cut down those trees that are marked by both foresters. How many will they cut down?
(A) 5
(B) 10
(C) 15
(D) 26
(E) 30
A4. Matic marks the trees: $3,6,9,12,15,18, \ldots$, Jure marks $5,10,15,20, \ldots$. They will both mark the 15th, 30th, 45th, 60th, and 75th tree, which is 5 trees.