Step1: Calculate $4^2$, $3^2+3^2$
$4^2=16$, $3^2+3^2=9+9=18$
Step2: Compare $4^2$ and $3^2+3^2$
$16 < 18$, so $4^2 < 3^2+3^2$
Step3: Classify $\triangle JKL$
Since the square of the longest side is less than the sum of squares of the other two sides, $\triangle JKL$ is acute.
Step4: Calculate $5^2$, $3^2+4^2$
$5^2=25$, $3^2+4^2=9+16=25$
Step5: Compare $5^2$ and $3^2+4^2$
$25 = 25$, so $5^2 = 3^2+4^2$
Step6: Classify $\triangle ABC$
Since the square of the longest side equals the sum of squares of the other two sides, $\triangle ABC$ is right.