Question 1170897
 Three friends A, B and C dine out and decide to split the bill according to what they order. 
 A's portion and B's portion of the bill totalled $35,
a + b = 35
 while B's portion of the bill was $5 less than C's portion of the bill.
b = c - 5
b - c = -5
 The ratio of A's portion to C's portion of the bill is 4:5.
{{{a/c}}} = {{{4/5}}}
Cross multiply
5a = 4c
a = {{{4/5}}}c
a = .8c
in the first equation, replace a with .8c, pair with the 2nd equation
b + .8c = 35
b - c  = -5
------------Subtraction eliminates b, find c
0 + 1.8c = 40
c = 40/1.8
c = $22.22
then
a = .8(22.22)
a = $17.78
find b
17.78 + b = 35
b = 35 - 17.78
b = $17.22
 Determine the total bill amount.
17.78 + 17.22 + 22.22 = $57.22