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simplify 36 - 4.5x + 36 to -4.5x + 72
simplify 102 - 7.5x - 60 to -7.5x + 42
add 7.5x to both sides
simplify -4.5x + 72 + 7.5x to 3x + 72
subtract 72 from both sides
simplify 42 - 72 to -30
divide both sides by 3
simplify 30/3 to 10
Answer: x = -10
To find percent error you use the following formula:

% error = (1.6 - 1.9)/1.9 * 100% = 15.79%
If 2 gallons of oil are used a day, than he will need 60 gallons of oil, because 30x2=60. For 60 gallons of oil, you would have to have 12 drums because 60÷5=12. Because there is already 8 drums of oil, there would already be 40 gallons because 8x5=40. If the owner already had 40 gallons of oil, they would only have to get 20 more gallons because 60-40=20. That would be 4 drums because 20÷5=4. The owner would have to order 4 more drums of oil.