Carry out the following operations as if they were calculations of experimental results, and express each answer

Question:

Carry out the following operations as if they were calculations of experimental results, and express each answer in the correct units with the correct number of significant figures:
(a) 7.310 km ÷ 5.70 km
(b) (3.26 x 10-3 mg) - (7.88 3 10-5 mg)
(c) (4.02 x 106 dm) + (7.74 x 107 dm)
(d) (7.8 m - 0.34 m)y(1.15 s 1 0.82 s)