let ice cream cost x
let candy cost y
x + y = 2.10 ........ equation 1
x = y + 0.80
apply ( x = y + 0.80 ) in equation 1
=> y + 0.80 + y = 2.10
=> 2y = 2.10 - 0.80
=> 2y = 1.30
=> y = 1.30 / 2 = 0.65
x = y + 0.80 = 0.65 + 0.80 = 1.45
so ice cream cost is $ 1.45 and candy cost is $ 0.65