Explanation

Let x represent crude oil inventory in millions of barrels for the previous week before the decline.”

Set up an Equation. “Crude oil inventory last week experienced a decline and result in the crude oil inventory now” becomes Oil inventory last week - decline in inventory = Oil inventory this week

x − 3.8 = 353.9

Solve the Equation. To isolate an unknown value x, add both sides of the equation by 3.8.

Original equation

x − 3.8 = 353.9.

Add both sides of the equation by 3.8.

x − 3.8 + 3.8 = 353.9+ 3.8

On the left, adding by 3.8 “undoes” the effect of subtracting by 3.8 and returns x. On the right, 353.9+ 3.8 = 357.7.

x = 357.7

The previous week, US crude oil inventory was 357.7 million barrels.

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