I supposed you mean similar and not congruent.
If kjn ≡ lmn, the kj would be equal to lm which in your question, is not
Assumed kjn is similar to lmn
scale = 17.5 ÷ 10 = 1.75
Therefore,
kj = 17.5 cm (given)
jn = 8 x 1.75 = 14 cm
kn = 6 x 1.75 = 10.5 cm
Perimeter = 17.5 + 14 + 10.5 = 42 cm
Answer: 42 cm