Answer:
Please see my attachment below.
It has the work to your question and should help you understand it visually.
Hope it helps.
Answer is 3 sweets. so 12 left out of 20. Sally took 3 times more than Sammy.
6.45 + 19.82 = c) 26.27
64.5 + 1.983 = a) 66.483
6.45 - 1.983 = b) 4.467
64.5 - 19.83 = d) 44.67