jmc

We can multiply the second equation by 5, so that our equations are $$\begin{array}{rl}5j-42k& =1\text{, and}\\ -5j+10k& =15.\end{array}$$Summing these equations gives $-32k=16$, so $k=-16/32=-1/2$. We substitute this value for $k$ into one of the equations to solve for $j$: $$\begin{array}{rl}2\left(\frac{-1}{2}\right)-j& =3\Rightarrow \\ j& =-4.\end{array}$$So the solution is $\boxed{(-4,-\frac{1}{2})}$.