help me solve this

6. [-I14.28 Points] DETAILS HUNTERDM3 4.1.0123. | MY NOTES ll PRACTICE ANOTHER l The following problem refers to strings in A, B, ..., Z. How many four-letter strings are there that begin with Y? ' weak 7. [-I14.32 Points] DETAILS HUNTERDM3 4.1.015. MY NOTES Use a decision tree to count the number of strings of length 3 using the symbols 5, t, and e with the restriction that at, at, and ta do not appear anywhere in the string. ' wank