Since the total cost of the sofa is $298
Since Katrina can pay 22$ per month for x months
Since she will pay $100 when she received it
Then the total cost of the sofa = 22x + 100
Equate this expression by the cost of the sofa
100 + 22x = 298
To solve the equation subtract 100 from both sides
100 - 100 + 22x = 298 - 100
0 + 22x = 198
22x = 198
Divide both sides by 22 to find x
x = 9
She can pay off the cost of the sofa in 9 months