To solve that question we must remember that
Then
[tex]\text{ LM = }\frac{\text{ AB + DC}}{2}[/tex]Using the value the problem gives, we get the following equation
[tex]4x+3=\frac{(x+8)+187}{2}[/tex]Solving that equation for x
[tex]\begin{gathered} 4x+3=\frac{(x+8)+187}{2} \\ \\ 8x+6=(x+8)+187 \\ \\ 7x=2+187 \\ \\ 7x=189 \\ \\ x=\frac{189}{7} \\ \\ x=27 \end{gathered}[/tex]The value of x is 27.