A 4x4 grid contains letters. Each letter has a value. The sum of values in each row and column are given. Determine the value of each letter.

Step 1: Assign variables to each letter and identify the equations from the grid.
Let Cy = $a$, R = $b$, C = $c$, T = $d$.
The grid has two unknown letters, which we will call $X_{3,4}$ (row 3, column 4) and $X_{4,3}$ (row 4, column 3).

The row sums are:

1. $a + b + a + d = 15 \implies 2a + b + d = 15$
2. $c + d + a + d = 23 \implies a + c + 2d = 23$
3. $b + c + b + X_{3