Ok, so the first triangle has a height of 5cm and a corresponding base of 8cm. That means These are the two legs, as they have a right angle between them. Area will be (5*8)/2 = 20cm²
The second triangle will be found like this:
What number times 20, and then divided by 2 equals 20?
Well, if we multiply 20*2 = 40, then divided by 2 = 20cm². So, the other leg is 2cm.