Express 0.000216 in scientific notation

Haruka hiked several kilometers in the morning. she hiked only 66 kilometers in the afternoon, which was 25% less than she had hiked in the morning. how many kilometers did haruka hike in all?

Will mark brainliest! ( explain the answer too, it can be one sentence)

Jeremy wants to determine the number of solutions for the equation below without actually solving the equation.