Let's denote the number of playlists on Ashley's app as x.
The number of playlists on Liam's app is 4 times the number of playlists on Ashley’s app, so it is 4x.
The total number of playlists on both apps is at least 45, so we can write the equation:
x + 4x ≥ 45
Combining like terms, we get 5x ≥ 45.
Dividing both sides of the inequality by 5:
x ≥ 9
So the solution set for x, representing the number of playlists on Ashley’s app, is x ≥ 9.