Please no links just the letter answer and explanation please

Answer:
-6.5 degrees/km
Step-by-step explanation:
I couldn't rlly find the answer myself, but this quizzis link has it. Question 7 on the quizzis btw https://quizizz.com/admin/quiz/5cbe6de57d6ff2001bf22fc3/2019-algebra-i-staar-review-day-2