How did use of violence william take control of england

When William the Conqueror became King of England in 1066 he introduced a new kind of feudal system into Britain. William confiscated the land in England from the Saxon lords and allocated it to members of his own family and the Norman lords who had helped him conquer the country.

the correct answer is history and tradition.

the perimeter of a triangle is 69 cm. side a is 5 cm shorter than side b. side c is twice as long as side a. find the length of each side. i need to know how to do it in 2 equations.  

equations:

a = b-5

c = 2a

a + b + c = 69