One reason the founders chose a federal system

The founders chose a federal system to balance the power of the central/national government with the individual rights of the states. This is so that the national government could do their job such as regulating the national economy, the military, and national laws. Also in addition to this, within the constitution according to the tenth amendment is that any right not given to the national government is given to the states or the people. This was a system of checks and balances out of fear that the central government could become to powerful just as the British governmental dictatorship under a king. As such they wanted as many rights and as little of control of government on peoples lives and if they did then the people would have a direct say in such an act. But remember the nation wasn't originally on the federal system originally it was run by the Articles of Confederation ran the government where there was only congress and no real power to the central government. States at that time were severely independent and it caused a flux in product prices leaving an imbalance in the states powers. Furthermore taxes could not be regulated, nor currency, and they would have to ask for a military. So the constitution under a federal system would allow for a stronger central government that could actually accomplish tasks to drive the nation forward and that it still was a well balanced system that didn't allocate too much power to one side.

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