<h3>every 3 weeks=21 days. this is because 21 is the lowest common factor of 7 and 3</h3><h3 /><h3>And you need to work on your spelling just saying</h3>
16 is the answer just add
1.37x + 1.08y = 16.36
x + y = 13
x = 13 - y
1.37* (13-y) + 1.08y = 16.36
17.81 - 1.37y + 1.08y = 16.36
1.08y - 1.37y = 16.36 - 17.81
-0.29y = -1.45
y = 5
x + 5 = 13
x = 13-5
x = 8
He bought 8 notebooks and 5 book covers
4(c+12)=2c+18
4c+12c=2c+18
4c-2c=18-48
2c=-30
c= -30/2
c= -15
