As given by the question
There are given that the base of the triangle is (4x) and the height is (2x+5).
Now,
From the formula of area of a triangle;
[tex]\text{Area of triangle=}\frac{\text{1}}{2}\times base\times height[/tex]Then,
Put the both value into the above formula
So,
[tex]\begin{gathered} \text{Area of triangle=}\frac{\text{1}}{2}\times base\times height \\ \text{Area of triangle=}\frac{\text{1}}{2}\times4x\times(2x+5) \\ \text{Area of triangle=}\frac{\text{1}}{2}\times4x(2x+5) \end{gathered}[/tex]Then,
[tex]\begin{gathered} \text{Area of triangle=}\frac{\text{1}}{2}\times4x(2x+5) \\ \text{Area of triangle=}\frac{\text{1}}{2}\times(8x^2+20x) \\ \text{Area of triangle=}\frac{(8x^2+20x)}{2} \\ \text{Area of triangle=}4x^2+10x \end{gathered}[/tex]Hence, the area of a triangle is shown below:
[tex]\text{Area of triangle=4x}^2+10x[/tex]