Plz answer plz plz plz

Tom can paint the fence in 12 hours, but if he works together with a friend they can finish the job in 8 hours. how long would it take for his friend to paint this fence alone?

Without any equipment, you can see stars that are 2{,}800{,}0002,800,0002, comma, 800, comma, 000 light-years away. by looking through a small telescope, you can see stars that are 3{,}112{,}000{,}0003,112,000,0003, comma, 112, comma, 000, comma, 000 light-years away. approximately how many times as far can you see using a small telescope as without any equipment?

If a + b = 28 and a - b = 10, then b =?