Iam not sure but i think this is the answer.

If someone is sre lets confirm it

No not exactly. He does not know C and X

Actually you can calculate for any given triangle 3 sides the area using the Herons formula. it goes like:

For and ABC triangle:

t=(A+B+C)/2 (so called semi-perimeter)

E = t x (t-A) x (t-B) x (t-C)

E = the area of the triabgle

So, if the area is ehat you search, then this is done with the Herons formula. If you need to calculate some height, as for example the attachment from serafino, you know the area and thus:

E = (C x H)/2 => H = 2E/C ...