Answer:
a) 2L + 2W = 42
b) L = 2W + 3
c) The system is :
2L + 2W = 42
L - 2W = 3
( add the two equations )
3L + (2w - 2w) = 45
3L = 45
L = 45/3
L = 15 ( Length )
15 - 2W = 3
2W = 15 - 3
W = 12/2
W = 6
