Hope this helps you, and good luck in the future :)
Answer:
57 mph
Step-by-step explanation:
were tryin to find its speed in the terms of mph which is miles per hour, so we need to find out how many miles it goes in a hour, so we divide 399 mph by 7 hours to get 57 mph.
I think it means like explain what are variable is. Only if your finding a variable: explain how you got the answer to that variable. Hope I helped!
Answer:
x=-36
Step-by-step explanation:
Add the 7/2x +1/2x to be 8/2x which means that it'll be 4x=18=9/2
then subtract 9/2x on both sides so itll be

-9/2x -9/2x
because if you do 8/2-9/2 it's -1/2
then multiply the reciprocal to both sides so

which then cancels out -1/2 and makes it
x=-36
the answer is 45
because I know 15+15=30 and 30+15=45
so 45-15=30
hope it helps :)