Can someone help me with this math problem please

Step-by-step explanation:
As the triangles are similar so,
3/9 = 4/12 = 4.5/k
Taking 3/9 and 4.5/k Then
[tex] \frac{3}{9} = \frac{4.5}{k} \\ \: cross \: multiply \\ k \: = \frac{9 \times 4.5}{3} \\ k \: = 13.5 \\hope \: it \: will \: help[/tex]