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Look at the sub-picture with the beef burger, and all the nodes which extend from it.  There are four options.  

Now look at the sub-picture with the chicken burger.  Same number of options.  

In fact, for each one of those sub-pictures, there are four options, one for each of the different choices of burger.  Well that is just exactly what multiplication counts: adding the same quantity a specified number of times.  Since each sub-picture is associated with 4 options and there are 3 sub-pictures, you can count the number of options as 3*4.

Now, if you didn't directly look at the four options, you could have counted the intermediate stage where you fries or salad.  Then you would have 3 sub-pictures corresponding to choice of burger, and 2options extending from that, a total of 6 options.  Then you could continue the logic, seeing that each burger-side choice then is associated with two options for a drink.  6 sub-pictures each extending to 2 options means 6*2 now counts the number of options.