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)