<h2>

**Answer:**</h2>

The the number of students who sign up for all three clubs = 6

<h2>

**Step-by-step explanation:**</h2>

The total number of students in the class is given by:

Total number of students= Number of students in poetry club+Number of students in history club+Number of students in writing club-Number of students in exactly 2 clubs-2×Number of students in all the three clubs.

Based on the information we have:

Total number of students= 59

Number of students in poetry club= 22

Number of students in history club= 27

Number of students in writing club= 28

and number of students in exactly two clubs=6

Let the number of students in the three club= x

Hence, we have:

59=22+27+28-6-2x

i.e.

59=71-2x

i.e.

2x=71-59

i.e.

2x=12

i.e.

x=6

**Hence, the answer is: 6**