Kayla had 64b dollars. she gave 1/8 of it to luke and spent $45. how much money did kayla have left? express answer in terms of b.

We know that
1) Kayla originally has 64b dollars
2) She gave 1/8 of it to Luke> (1/8)*64b=8b
in this moment Kayla has> 64b-8b=56b
3) Kayla spent $45
in this moment Kayla has> 56b-$45

therefore

the answer is
(56b-$45)

the amount of money Kayla had initially = 64b
             
the amount of money she gave Luke is 1/8th of what she had.
                                                                                   
the amount she gave Luke - 64b x 1/8 = 8b
                       
then amount she had remaining after giving Luke - 64b - 8b = 56b
                                                                               
from the amount she had after giving Luke she spent 45 therefore amount Kayla had left = 56b - 45

Definitely