If ƒ(x) = 2x, then ƒ -1(x) = a)-2x b)½x c)x - 2

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!