If you would like to solve y = x - 4 and 2 * x + y = 5, you can do this using the following steps:
y = x - 4
2 * x + y = 5
_____________
2 * x + (x - 4) = 5
2 * x + x = 5 + 4
3 * x = 9 /3
x = 9 / 3
x = 3
y = x - 4 = 3 - 4 = -1
The correct result would be x = 3 and y = -1.
Answer:
the first 100 digits of pi are 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679
15.25 divided by 100= 0.1525 times 15 = 2.2875 then round to $2.29 (2.29 is the tip) 2.29 + 15.25 = $17.54 would be the total cost!
You may write them separating the units and tens digits, and then use FOIL to add 4 easy tems. For example, let's compute 
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