Answer:
b = 3.1
Step-by-step explanation:
Since the length of one of the longer sides, a, has been given to be 6.3, plug it into the equation.
2(6.3) + b = 15.7
12.6 + b = 15.7
b = 15.7 - 12.6
2
<em>good luck, i hope this helps :)</em>