Matilda throws a dice 70 times work out the estimate for the number of sixes she should expect to throw

So she is finding an experimental probability.

experimental probability=(number specific outcomes observed)/(total observations)

In this case:

ep=(number of sixes rolled)/(number of rolls)

ep=(number of sixes rolled)/70

After she calculates the expected probability then she would approximate the number of expected sixes to be rolled by:

ep*rolls=(expected number of sixes rolled in n rolls)