Question 856603
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Hi,
The total number of $10 bills and $20 bills is 7 more than the number of $5
 y + z = x + 7
-7 + (y +z) = x
<u>35 - (y +z)</u> = x
  28 = 2x
  14 = x, number of $5 bills
(y + z) = 21 , y = {{{ 21-z}}}
5x+10y+20z=370   |Yes! Now substitute
 $90 + $10(21-z) + $20z = $370
  $90 + $210 + $10z = $370
           $10z = 70 
             z = 7,  number of $20 bills. There are 14 $10 bills
CHECKING our answer***
 $90 + $140 + $140 = $$370
Wish You the Best in your Studies.