Area for triangle =bh/2
if we draw a line through the middle of the triangle we can make it a right angle triangle and use it to work out the height with pythagoras.
If we half the triangle then a=7 and b will be 25 and b is the hypotenuse so to find the height we do root 25^2-7^2=24 so the height is 24 and if we work back and do 7 squared plus 24 squared and root the answer we get 25