Selma = 12 +   boxes, where "t" is the time in minutes.


Trudy = 18 +   boxes.


Your equation is


    Selma = Trudy,


or, equivalently,


    12 +  = 18 + .


Your task is to find "t" from this equation.


First step is to write it in this form


     -  = 18 - 12 = 6.


Next step is to multiply both sides by 35.