Bethany knits hats and scarves. A hat takes her 1.5 days, and a scarf takes her 4 days. Bethany recently spent 18 days knitting 7 items. Write and solve the system of equations to find the number of hats (h) and the number of scarves (s) that Bethany knit.
a) 5 hats, 2 scarves
b) 4 hats, 3 scarves
c) 3 hats, 4 scarves
d) 2 hats, 5 scarves