How Many Hours for an 80?

A music teacher logged how many hours each student practised (hours) and their exam mark (marks). A new student asks: how many hours should I practise to be predicted a mark of target?

Write hours_for_mark(hours, marks, target).

• Fit a LinearRegression model with hours as the only feature.
• The fitted line is mark = coef_ * hours + intercept_. Find the number of hours where this line equals target.
• Return that number of hours, rounded to 2 decimal places, as a plain float.

The fitted slope is never zero in the tests. The answer may be outside the range of hours in the data, or even negative. Return it anyway.