Respuesta :

[tex]\bf \textit{area of a triangle}\\\\ A=\cfrac{1}{2}bh~~ \begin{cases} b=3x+5\\ h=5x \end{cases}\implies A=\cfrac{1}{2}(3x+5)(5x) \\\\\\ A=\cfrac{1}{2}(15x^2+25x)\implies A=\cfrac{15x^2+25x}{2}[/tex]