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.
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.