The area of the triangle is:

You can easily find the area of a triangle using the formula:

Where h is the height of the triangle, and b the base.
Looking at the figure we can see that h = 7, but we need to discover the base, we know that the base is:

Where:

Therefore, our base length is:

Then we can just apply the formula for the area:

I hope you liked it
Any doubt? Write it in the comments and I'll help you