A student's marks in six subjects are recorded as follows:
Physics: $78$, Chemistry: $82$, Mathematics: $90$, Biology: $74$, English: $68$, Computer: $86$.
If the minimum passing marks are $70$ in each subject, what percentage of the total subjects did the student fail in?

Let's calculate step-by-step:
* Total number of subjects = $6$
* Minimum passing mark per subject = $70$

Let's check the scores to identify failed subjects (score $<70$):

1. Physics: $78\ge 70$ (Pass)
2. Chemistry: $82\ge 70$ (Pass)
3. Mathematics: $90\ge 70$ (Pass)
4. Biology: $74\ge 70$ (Pass)
5. English: $68<70$ (Fail)
6. Computer: $86\ge 70$ (Pass)

Number of subjects failed = $1$ (English).

Calculate the failure percentage:

$$\text{Failure Percentage}=\left(\frac{\text{Number of failed subjects}}{\text{Total number of subjects}}\right)\times 100\%$$

$$\text{Failure Percentage}=\frac{1}{6}\times 100\%\approx 16.67\%$$