Calculate the missing value A the amount in her online shopping basket, Determine the selling price of one t-shirt, Write down a formula that can be used to calculate the total income received, and Calculate the missing value B.

Value A represents the total cost for Vinyl. This is calculated by multiplying the amount of Vinyl by its price per unit.

$$A = \text{Amount of Vinyl} \times \text{Price per unit of Vinyl}$$ $$A = 5 \times \text{R}160.40$$ $$A = \text{R}802.00$$

We can also verify this using the total payable:

$$\text{Total Payable} = \text{Total for White T-shirts} + A$$ $$\text{R}14\,000 = \text{R}13\,198.00 + A$$ $$A = \text{R}14\,000 - \text{R}13\,198.00$$ $$A = \text{R}802.00$$

The missing value A is $\boxed{\text{R}802.00}$.

From TABLE 1, we can use the 'Revenue (Rand)' for a given 'NUMBER OF TSHIRTS'. For example, for 25 t-shirts, the revenue is R2250.

$$\text{Selling price per t-shirt} = \frac{\text{Total Revenue}}{\text{Number of T-shirts}}$$ $$\text{Selling price per t-shirt} = \frac{\text{R}2250}{25}$$ $$\text{Selling price per t-shirt} = \text{R}90$$

Let's check with another data point, e.g., 50 t-shirts and R4500 revenue:

$$\text{Selling price per t-shirt} = \frac{\text{R}4500}{50} = \text{R}90$$

The selling price of one t-shirt is $\boxed{\text{R}90}$.

Total income is the total revenue. Based on the selling price calculated in Step 2, the formula for total income is the selling price per t-shirt multiplied by the number of t-shirts.

$$\text{Total Income} = \text{Selling Price per t-shirt} \times \text{Number of T-shirts}$$

Using the selling price of R90:

$$\boxed{\text{Total Income} = \text{R}90 \times \text{Number of T-shirts}}$$

The problem states that the total expenses can be calculated by the formula: $\text{Expenses} = \text{R}70 \times \text{number of t-shirts}$.
From TABLE 1, the missing value B corresponds to 50 t-shirts.

$$\text{B} = \text{R}70 \times \text{Number of T-shirts}$$ $$\text{B} = \text{R}70 \times 50$$ $$\text{B} = \text{R}3500$$

The missing value B is $\boxed{\text{R}3500}$.