Answer :

Sure! Let's solve each of these equations step by step.

### 1. Solving [tex]\(\frac{3}{4} x = 9\)[/tex] for [tex]\(x\)[/tex]:

First, isolate [tex]\(x\)[/tex]:

[tex]\[ \frac{3}{4} x = 9 \][/tex]

Multiply both sides by [tex]\(\frac{4}{3}\)[/tex] to get [tex]\(x\)[/tex] alone:

[tex]\[ x = 9 \times \frac{4}{3} \][/tex]

Simplifying the right side:

[tex]\[ x = 12 \][/tex]

### 2. Solving [tex]\(a + x = b\)[/tex] for [tex]\(x\)[/tex]:

We need to express [tex]\(x\)[/tex] in terms of [tex]\(a\)[/tex] and [tex]\(b\)[/tex]:

[tex]\[ a + x = b \][/tex]

Subtract [tex]\(a\)[/tex] from both sides to isolate [tex]\(x\)[/tex]:

[tex]\[ x = b - a \][/tex]

### 3. Solving [tex]\(c x = d\)[/tex] for [tex]\(x\)[/tex]:

We need to express [tex]\(x\)[/tex] in terms of [tex]\(c\)[/tex] and [tex]\(d\)[/tex]:

[tex]\[ c x = d \][/tex]

Divide both sides by [tex]\(c\)[/tex] to isolate [tex]\(x\)[/tex]:

[tex]\[ x = \frac{d}{c} \][/tex]

### 4. Solving [tex]\(a + 5 x = 7 x - r\)[/tex] for [tex]\(r\)[/tex]:

First, let's simplify and isolate [tex]\(r\)[/tex]:

[tex]\[ a + 5 x = 7 x - r \][/tex]

Subtract [tex]\(5 x\)[/tex] from both sides:

[tex]\[ a = 7 x - 5 x - r \][/tex]

Which simplifies to:

[tex]\[ a = 2 x - r \][/tex]

Add [tex]\(r\)[/tex] to both sides:

[tex]\[ a + r = 2 x \][/tex]

Subtract [tex]\(a\)[/tex] from both sides to isolate [tex]\(r\)[/tex]:

[tex]\[ r = 2 x - a \][/tex]

### Summary:

Combining all these results, we get:

1. [tex]\( x = 12 \)[/tex]
2. [tex]\( x = b - a \)[/tex]
3. [tex]\( x = \frac{d}{c} \)[/tex]
4. [tex]\( r = 2 x - a \)[/tex]

So, the solutions to the given equations are:

[tex]\[ (x, x \text{ in terms of } a \text{ and } b, x \text{ in terms of } c \text{ and } d, r \text{ in terms of } a \text{ and } x) = (12, b - a, \frac{d}{c}, 2x - a) \][/tex]