Algebra 2 helpppp...pllzzzzz?

Question

1.) What number, when added to the numerator and denominator of 7/9, changes it to a fraction equivalent to 6/7?

7
5
4

2.) A boat can travel at 21 mph in still water. It travels 72 miles downstream with the current in three hours, then returns upstream the same distance against the current in four hours. What is the speed of the current? (Set up the grid, fill in known information, think about which quantities are equal, and set them equal in an equation.)

3 mph
4 mph
5 mph

3.) A small heater can heat a room in 15 minutes. A larger heater can heat the same room in 10 minutes. How long will it take to heat the room if they both work together? (This can still be figured on the basis of 1 hour: How much will each do in 1 hour? The small heater will do 4 rooms @ 15 min. each and the larger will do 6 rooms @ 10 minutes each. Add what each can do in 1 hour and set it equal to the number of rooms they can do together in one hour. After you get the number of rooms they can do together in one hour, simplify to find how long it takes to do one room)

3 minutes
6 minutes
7 minutes

Thanks for all your help...

Answer 1

1.

let the number is  = x

the addition of the number  = x + 7/9

the fraction of the number equivaient  x + 7/9 = 6/7

                      x + 7/9 = 6/7

 subtract the both side in 7/9

                      x+ 7/ 9 -7/ 9 = 6/ 7 -7/ 9

   7 ,9 lcm is  63

                     x =( 54 -49 )/ 63

                    x = 5/ 63

 therefore the  numerator added 5