Please help me on this question

$$\small{\text{Geometric sequence : $ a_1=a,\ a_2=a*r,\ a_3=a*r^2,\ a_4=a*r^3,\ a_5=a*r^4,\ \dots $ }}\\ \small{\text{ $ a_1=a=3 \qquad a = 3 $ }}\\ \small{\text{ $ a_4=a*r^3 = 3*r^3 =192 \qquad 3*r^3 =192 \qquad r^3 =64 \qquad r =4 $ }}\\ \small{\text{ $ a_3=a*r^2 = 3*4^2 = 3*16 = 48$ }}$$