This is a 3-4-5 triangle.
Remember,
SOH-CAH-TOA
S(ine) = O(pposite)/H(ypotenuse)
C(osine) = A(djacent)/H(ypotenuse)
T(angent) = O(pposite)/A(djacent)
In Cosine, the adjacent = 3, and the Hypotenuse = 5
Hypotenuse is the longest side.
3,4,5 is the triangle that fits inside, therefore, the Opposite is 4, and Adjacent is 3
T(angent) = O(pposite)/A(djacent)
Plug in the numbers
T = 4/3
tan = 4/3 is your answer
hope this helps