Let's solve the problems step by step.

### Bài 3 - 91 (14)

We need to find \( x \):
\[
(x + 1) + (x + 4) + (x + 7) + \ldots + (x + 28) = 156
\]

**Step 1: Identify the series.**

The series consists of terms increasing by 3 from \( x + 1 \) to \( x + 28 \). The series can be rewritten as:
\[
n \cdot x + \text{constant sum}
\]

**Step 2: Count the terms.**

The first term is \( 1 \) (corresponding to \( x + 1 \)) and the last term is \( 28 \). The sequence goes like: \( 1, 4, 7, \ldots, 28 \), where the first term \( a = 1 \), common difference \( d = 3 \).

To find the number of terms \( n \):
\[
a_n = a + (n-1)d
\]
Setting \( a_n = 28 \):
\[
28 = 1 + (n-1) \cdot 3
\]
\[
27 = (n-1) \cdot 3
\]
\[
n-1 = 9 \implies n = 10
\]

**Step 3: Sum the constants.**

The constant terms are:
\[
1 + 4 + 7 + \ldots + 28
\]

This is an arithmetic series with \( n = 10 \):
\[
S_n = \frac{n}{2} (a + l) = \frac{10}{2} (1 + 28) = 5 \cdot 29 = 145
\]

**Final equation:**
\[
10x + 145 = 156
\]
\[
10x = 11 \implies x = 1.1
\]

### Bài 4 - 92 (14)

We need to compute:
\[
\frac{2006}{2008} \times \frac{2001}{2004} \times \frac{2008}{2002} \times \frac{2004}{2006} \times \frac{1001}{2001}
\]

**Step 1: Simplify the fractions.**

We have:
\[
\frac{2006 \times 2001 \times 2008 \times 2004 \times 1001}{2008 \times 2004 \times 2002 \times 2006 \times 2001}
\]

**Step 2: Cancel common terms.**

After canceling \( 2006, 2008, 2004, 2001 \):
\[
\frac{1001}{2002}
\]

### Result:

Thus, we get:
\[
\frac{1001}{2002} = \frac{1}{2} \quad (\text{since } 1001 = \frac{2002}{2})
\]

### Bài 5 - 93 (14)

We need to write the sum of the three fractions so that one of the denominators equals 1.

Let's denote the fractions:
1. \( \frac{a_1}{b_1} \)
2. \( \frac{a_2}{b_2} \)
3. \( \frac{a_3}{b_3} \)

To combine these fractions, we would find a common denominator, typically \( b_1 \cdot b_2 \cdot b_3 \).

The task seems to be explaining a process rather than calculating directly, but generally, this involves the least common multiples or similar to combine and then simplify.

Let me know if you need further clarification or additional problems!