Answer :

840 - 3/7(840) =
840 - 360 = 480

480 - 1/8(480) = 
480 - 60 = 420

I. 3·840/7=3·120=360$  spent

840-360=480$ rest

II.1·480/8=60$ spent

480-60=420$ left

Answer:420$

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