since we know that 40% = $20. we can understand that 80% = $40. since books and savings combine to 40%. this means books and savings mean $20. now that we have found how much 80% of money she has. we can find the remaining. 100% - 80% = 20%. we can divide our ratio 40% = $20 by 2 too see how much money is 20%. in which is %10
now we add up and get $50 in total.
hope this helps :D
