Question

If it has rained 306mm in last 3 days, how many (mm) of rainfall will be
there in one week (7 days)?!

Answer 1

Let the number of days be "x"

$306=3x\\x=\frac{306}{3} =102$

Thus,

$7x=102*7\\7x=714$

It will rain 714 mm in a week.