Because it is 3:4:5, the triangle is a right triangle, and the straight sides are 15 and 20, so the area is 15×20÷2= 150cm?
2、35×2.6÷(3.9×56)=35×2.6÷3.9÷56=35÷56×2.6÷3.9=5/8×2/3=5/ 12
3. Wash for one hour110, then 40 minutes =2/3 hours, so115.
4. Same as the first question