1, the three sides of the triangle are: 60×3/(3+4+5)= 15, 60× 4/(3+4+5) = 20,60× 5/(3+4+5) = 25.

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