Let x be the cost of 1kg of sugar and y = cost of 1 kg of flour
We have these two equations
3x + (1/2)y = 9.40
6x + 2y = 20.20
Multiply the first equation by -2 and add to the second
-6x - y = -18.80
6x + 2y = 20.20
______________
y = 1.40 = the cost of 1 kg of flour
+16 
