The area of a parallelogram is the product of the base and the altitude. in this case
[tex]a(7+a)=30[/tex]then solve the equation
[tex]\begin{gathered} a(7+a)=30 \\ 7a+a^2=30 \\ 7a+a^2-30=30-30 \\ a^2+7a-30=0 \end{gathered}[/tex][tex]\begin{gathered} \mleft(a-3\mright)\mleft(a+10\mright)=0 \\ a-3=0\quad \mathrm{or}\quad \: a+10=0 \\ a=3,\: a=-10 \end{gathered}[/tex]therefore:
altitude = 3
base = 3 + 7 = 10