Add or subtract as indicated:

a. 5.80×10^9s + 3.20×10^8s
b. 4.87×10^-6m - 1.93×10^-6m
c. 3.14×10^-5kg + 9.36×10^-5kg
d. 8.12×10^7g - 6.20×10^6g

How do I solve these?