Does anyone know the answer what to add and multiply because i really don't get it

Trevor and marissa together have 26 t-shirts to sell. if marissa has 6 fewer tshirts that trevor, find hiw many tshirts trevor has. identify the if-than moves in your solution

Imagine a new pasture with grass growing on it. every day after the seeds have germinated, the number of blades of grass in the pasture triples. after 18 days, the entire pasture is completely covered in grass. how many days did it take for the pasture to be one-third covered in grass?

Tom wants to order tickets online so that he and three of his friends can go to a water park the cost of the tickets is 16.00 per person there is also a 2.50 one-time service fee for ordering tickets online write an expression in term of n that represents the cost for n ordering tickets online