When two expressions are equal, the number sentence is an equation. jolie bought 3 hot dogs for $1.59 each and 3 orders of fries for x dollars each. she spent $7.74. what is the cost of one order of fries?

If she bought 3 hot dogs for $1.59 each, then she spent $4.77 on the hot dogs.  If she spend a total o $7.74 total, and she spent $4.77 on hot dogs, that means that she spent $2.97 on the fries.  An equation for this would be 3x = 2.97.  Divide both sides by 3 to solve for x, a single order of fries.  x = .99