Answer:
x = 0, y = 4
Explanation:
1 pen = x dollars
4 pen = 4x
1 ruler = y dollars
5 rulers = 5y
now,
a) = 5y + 4x = 20
2x + 4y = 16
Now,
2x + 4y = 16
or, 2x = 16 - 4y
or, x = (16 - 4y)/2
Now,
5y + 4x = 20
or, 5y + 4{(16 - 4y)/2} = 20
or, (10y + 64 - 16y) = 40
or, 64 - 6y = 40
or, 64 - 40 = 6y
or, 6y = 24
so, y = 4
now,
x = (16 - 4(4))/2
or, x =(16 - 16)/2
so, x = 0