When performing enzyme kinetics measurements, you mix your enzyme and substrate then monitor the progress of the reaction over time (either the disappearance of substrate or appearance of product, let's say in this example that you are looking at the appearance of product). If you plot the amount of product formed v. time, you will see a curve that goes up and slowly levels off as the reaction nears completion/equilibrium. The Michaelis-Menten equation is concerned with the initial reaction rate. So, when you look at the data, you want to look only at the first few data points of the [product] v. time graph, fit it to a line and record the slope. Now you have one data point for your Michaelis-Menten curve (a concentration of substrate, [ S], and the corresponding initial reaction velocity, vo). You would then repeat these kinetic measurements and determine vo for different concentrations of substrate while keeping other factors such as concentration of enzyme and temperature constant.
So, the slopes that you are given correspond to the initial reaction velocities (vo).