1. 75
2. 75
3. 900
For the first one, add 10 + 15, then times it by 6 (the height). Finally, divide by 2. Base + base times height divided by 2.
The second one, do 15 x 10, then divide by 2. Base x height divided by 2
Finally, the last one do 36 x 35. Base x height.