if a is equals to matrix 2 4 -1 ke if a is equals to matrix of 24 - 1 k and a square is equal to zero find the value of k ​

The first week samantha learned to read braille, she could read 10 words per minute. in the second week she increased her speed by 20%. in the third week she increased her speed again by another 25%. how many words could she read per minute by the third week? hurry and tell me!