Answer:
4 [miles].
Step-by-step explanation:
1) the condition 'the entire trip took 5 hours' can be written as (where t_us - time spent upstream, t_ds - time spent downstream)

2) but the distance [D] upstream is equal the distance downstream, then the condition above can be written:

3) finally,

D=5*4/5=4 [miles].
The answer is b because the ratio is blondes to brunettes.
I'm sending you two screenshots of the explanation I hope this helps.
Answer:
slope of line ax + by = c is -a/b
so, slope of 7x +2y =5 is -7/2