Let A₁, A₂, A₃, A₄ be the 4 AM Between 4 And 19

Then, 4, A₁, A₂, A₃, A₄, 19 are in AP

We know,

A_n = a + (n - 1)d

a_{6 =} 19 = 4 + (6 - 1)d

d = 3

Hence,

A₁ = a + d = 4 + 3 = 7

A₂ = A1 + d = 7 + 3 = 10

A₃ = A2 + d = 10 + 3 = 13

A₄ = A3 + d = 13 + 3 = 16