We can solve this problem by using the law of sines.
The law of sines states that the ratio of the length of a side of a triangle to the sine of the angle opposite that side is the same for all sides and angles in a given triangle.
Using this law on our problem, we have the following relation
![(j)/(\sin J)=(i)/(\sin I)](https://img.qammunity.org/2023/formulas/mathematics/college/1rhnnihdz6hames81kbe364le54roezkdf.png)
We know the measure of 3 of those values. Plugging those values on this equation, we have
![\begin{gathered} (j)/(\sin 34^(\circ))=(206)/(\sin 72^(\circ)) \\ j=(206)/(\sin72^(\circ))\cdot\sin 34^(\circ) \\ j=121.121864097\ldots \\ j\approx121.1 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/jdcy193fa33hy4agj226dz624pbikni7pc.png)
The length of j is 121.1.