The angle θ lies in Quadrant I.

4/3     

Here's an explanation...

Let's find  sin θ  using the Pythagorean identity.

sin²θ  +  cos²θ   =   1

sin²θ  +  (3/5)²   =   1

sin²θ   =   1 - (3/5)²      sin is positive in Quad I , so take the positive sqrt of both sides.

sin θ   =   √[ 1 - (3/5)² ]

sin θ   =   4/5

And...

tan θ   =   sin θ / cos θ   =   (4/5) / (3/5)   =   4/3