Answer:
[tex]\large \boxed{27}[/tex]
Step-by-step explanation:
Cost of sofa = $540
-Deposit = 0.15 × $540 = 81
Balance owing = $459
[tex]\text{No. of months} = \text{\$459} \times \dfrac{\text{1 mo}}{\text{\$17}} = \textbf{27 mo }\\\\\text{They will need to make $\large \boxed{\mathbf{27}}$ monthly payments.}[/tex]