The earliest people in Texas arrived during what era

Their arrival marks the beginning of the Paleolithic Era in Texas – the first of three time periods between the arrival of those first people and the arrival of European explorers: The Paleolithic Era (until about 6000 B.C.), the Archaic Era (6000 B.C. to A.D. 700), and the Late Prehistoric Period (A.D. 700-A.D. 1500).The earliest Texans lived as hunters and gatherers, sharing the landscape with ice age animals including mammoths, cave lions, giant sloths, and dire wolves.

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