Can someone tell me how to add and subtract fractions with unlike denominators, i've been having trouble for 2 years, and still do not understand.

Calculate the density of benzene if 300ml of it weighs 263g. a. 0.88 g/ml b. 1.14 g/ml c. 78,900 g/ml d. 37 g/ml

Currently, the largest cruise ship has a tonnage of 225,282 gross tons (gt). which of the following is a reasonable estimate for the tonnage of this cruise ship? a. 2 × 10^5 gt b. 2 × 10^6 gt c. 2 × 10^-5 gt d. 2 × 10^-6 gt

What’s the answer? and how do i solve it ?