At an airport, two business partners both walk at \(1.5 \mathrm{~m} / \mathrm{s}\) from the gate to the main terminal, one on a moving sidewalk and the other on the floor next to it. The partner on the moving sidewalk gets to the end in \(60 \mathrm{~s}\), and the partner on the floor reaches the end of the sidewalk in \(90 \mathrm{~s}\). What is the speed of the sidewalk in the Earth reference frame?