From the question we know that Maria and Josie went to the movies and spent a total amount of money, which should be the price of the tickets added to the price of the snacks.
Knowing that the price of the snacks is $3.75 and the price of the tickets is t, it looks like all that is left is to assign a variable to the total amount of maney they spent at the movies and write out the equation.
If we let the total amount of money they spent be x, then x= t+3.75, whcih should be your answer!
Let's call the number you thought of n. Then what the two steps you took can be written as an equation:

Subtract n to get all of your variables to one side:

At this point, I recommend turning your mixed number into an improper fraction. It will make things easier later on:

Now divide both sides by 11 to get the value of n:
A² + b² = c²
a² = c² - b²
a² = 9² - 6²
a² = 81 - 36
a² = 45
a = √45
a ≈ 6.7082
a = 6.7
Step-by-step explanation:
x -0.1x = x(1-0.1) = 0.9x