The sun burns 6 million tonnes of hydrogen a second. calculate how many tonnes of hydrogen it burns a year (that's 365.25 days)

Your answer is 189,345,600,000,000 tons per year

There are 86,400 seconds in a day, and 365.25 days in a year. So 86,400*365.25= 31,557,600 seconds per year. Now if each second the sun burns 6 million tons we have to multiply that by the number of total seconds per year. So 31,557,600 * 6,000,000= 189,345,600,000,000 hydrogen tons per year.
Hope this helped :)

No because if you do the higher number minus the lower number you will get a positive. if you do it the other way around you will get a negative number