Find the length of x for an arrow head

Question

I am struggling to get some traction on this and need someone to show me how to calculate this. I have a GCSE question that asks:

In the attached image I'm being asked the following:

The arrowhead has an area of $3.6cm^2$. Find the length $x$.

Answer 1

The area $3.6cm^2$ is the area of the larger triangle minus the area of the smaller triangle.

$1.5\cdot h - 1.5\cdot (h - x) = 3.6$

$1.5h - 1.5h + 1.5x = 3.6$

$1.5x = 3.6$

$x = 2.4$cm

Answer 2

Hint

You can divide the area in two triangles. You can consider $x$ as the basis and thus the height is $1.5$ cm.