I don't understand how to calculate initial rates of reaction based on experimental data

The experimental data given in the question will serve as a basis for comparison when answering the question. You must compare the initial rates of reaction given to the concetrations of the rectants. For example, you may see that the concebtratiohn of reactant A remains constant while the concentration of reactant B increases, yielding the same initial rate of reaction. This means that the [B] does not affect initial reaction rate and can discount it from further calculations. You can then go back and look at the data, only deducing how the [A] affects the initial rate of reaction. For example, if the concentration of A doubles and the initial rate of the reation also doubles, you can assume a linear relationship i.e. of order 1. If the concentration of A doubles and the initial rate of reaction quadruples, you can assume an exponential relationship i.e. of order 2. 

Let's look at a few examples.