A shop sells laptops at $600 each and a smartphone at $400.  Celine buys two laptops and four smartphones for her children. How much change does she get back if she has $3000?
The cost of the two laptops is 2 x $600 = $<T>multiply(2, 600)=1200
The cost of the four smartphones is 4 x $400 = $<T>multiply(4, 400)=1600
Thus, the total cost of all the items is $1200 + $1600 = $<T>add(1200, 1600)=2800
Therefore, Celine gets a change of $3000 - $2800 = $<T>subtract(3000, 2800)=200
