Lucas had some money. He spent $55 on some files, 1/6 of the money on
some books and 1/10 of the remaining money on stationery. He saved the rest
of the money. If he saves $90,
(a) how much money did he have at first?
(b) what fraction of his money did he save?
$55 + $100 = $155
155 + 31 = 186
90/186 = 15/31