Answer:
The answer is A.
Go to desmos and type your equation in
Using simultaneous equation,
a=-1, b=1, x=1, y=0
OR
a=1, b=-1, x=1, y=0.
Let m be the distance (in miles) she runs in a month
and w be the distance (in miles) she runs in a week
since the total distance she run in a week is one third of what she run in a month, in equation form
w = m/3
to calculate the distance she run in a month,
m = 3w
m = 3(6 miles)
m = 18 miles in a month