What is a stalemate and why did one develop on the Western Front?

A stalemate is a long period of stagnation in a war, in which neither side makes significant advances. The stalemate at Marne between the “Entente” (British and French) and German forces was due to their equal size and strength and to the use of new deadly weaponry, which drove each army to barricade themselves in trenches.

Explanation:

the noble might have thought that the system was far because they had lot of things and riches and the serf would have thought that the feudal system was un fair because of the way they were treated.

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