Substitute the value of p=6 into the formula:

\begin{aligned} q &= 4p-6 \\ q &= 4\times6-6 \\ q&=24-6 \\ q &= 18 \end{aligned}

Substitute the values h = 1.6 and m = 80 into the formula:

\begin{aligned} \text{BMI} &= \dfrac{80}{1.6^2} \\[1.5em] \text{BMI} &= \dfrac{80}{2.56} \\[1.5em] \text{BMI} &= 31.25\end{aligned}

So the person has a BMI of 31.25

There are 2 more green sweets than there are red sweets, and there are x red sweets. So the number of green sweets is:

x+2

So there are 3 blue sweets, plus x red sweets, plus x+2. Combining these gives the following expression:

3+x+(x+2)

Which can be simplified by collecting like terms to:

5+2x

The amount of sodium lost (S) can be found by multiplying the loss per litre by the number of litres lost (W):

S=1.1\times W

The amount of water lost (W) can be found by multiplying the loss per hour by the time spent exercising (t):

W = 1.5 \times t

Now we need to combine the two expressions by substituting our expression for W into our expression for S:

\begin{aligned}S &= 1.1 W \\ S &=1.1 \times (1.5t)\\ &=S= 1.65 t \end{aligned}

Our formula needs to add the base cost of £40 to the hourly rate of £9.50. Our formula is therefore:

C = 40 + 9.5h

If the plumber earns £68.50 in a single repair job, we can substitute this into our formula and rearrange to get h:

\begin{aligned} 68.5 &= 40+9.5h \\ (-40)\quad 28.5 &= 9.5 h \\ (\div9.5)\quad  3 &= h \end{aligned}

So the repair job took 3 hours.