Question 1125005
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From the condition, you have this system of 2 equations


L - F = 84         (1)

{{{(1/5)*L}}} = {{{(3/8)*F}}}.     (2)


To solve it, first multiply eq(2) by 5 (both sides). You will get


L = {{{(15/8)*F}}}.         (3)


Now substitute expression (3) into eq(2). You will get


{{{(15/8)*F}}} - F = 84,

{{{(7/8)*F}}} = 84  ====>  F = {{{(8/7)*84}}} = 96.


Hence, Fiona saved 96 dollars.


Then Lauren solved  84 + 96 = 180 dollars.


Together, they saved  180 + 96 = 276 dollars.
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Solved.