In a parallelogram, opposite angles are congruent. This means that we can write the following equations:
[tex]\begin{gathered} 3x+26=4x \\ and \\ 7y-1=5x+21 \end{gathered}[/tex]
solving for x and for y we get:
[tex]\begin{gathered} 3x+26=4x \\ \Rightarrow26=4x-3x=x \\ x=26 \\ ------------------------ \\ 7y-1=5y+21 \\ \Rightarrow7y-5y=21+1=22 \\ \Rightarrow2y=22 \\ \Rightarrow y=\frac{22}{2}=11 \\ y=11 \end{gathered}[/tex]
therefore, x = 26 and y = 11
