Mary and John have both completed a trip up an escalator. John took 15 steps on the way up and took 12 seconds to reach the top. Mary took o

Let the number of steps be x.

 

then John goes up   x-15   steps in 12 seconds

and Mary ....

 

 

You can finish it.

You can also solve for the RATE of the stairs, r

   then r * t    +   stairs taken = #stairs

 

John     15 + 12 r = #stairs

Mary       7 + 18r = # stairs

                  15 + 12r = 7+ 18r      now you can solve for r     

                                      then use r in either of the equations to calc #stairs