Using scientific notation, what is the solution to (8 * 104) + (7.2 * 103)?

8.72 * 104

8.72 * 103

87.2 * 104

15.2 * 104

Robin spent 25% more time on his research project than he had planned he’s been an extra h ours on the project which of the following expressions could represent the number of hours rob actually spent on the project