Which statement explains why britain became a part of the roman empire much later than nearby gaul

The statement that explains why Britain became a part of the Roman Empire much later than nearby Gaul is that the channel of water between Britain and Gaul was an obstacle.
The Romans didn't find it easy to cross these huge amounts of water, which is why their conquering of Britain came later than nearby Gaul. 

Find out the  what was the original price of her purchase .

To prove

Let us assume that the original price of her purchase be x.

As given

A store is having a 20%-off sale on all merchandise. If Mai buys one item and saves $13 .

20% is written in the decimal form.

= 0.20

Than the equation becomes

x × 0.20 = 13

x = $65

Therefore the original price of her purchase is $65.