Multi-Dimensional Arrays With Indexes

This does not apply to the task itself, but to the topic as a whole.
I do not quite understand the principle of calculation For example, if the task will be myData is equal to 13, then how to calculate it?

const myArray = [ [1, 2, 3], [4, 5, 6], [7, 8, 9],
[[10, 11, 12], 13, 14], ];
const myData = myArray[?][?];

what exactly you want to calculate mean , describe in detail

Try it, what do you think it could work?