b) The 6 faces of a solid cube of length 3 m is to be painted. The painting cost is ksh 150 per square metre. Find the total cost of painting the cube.

Urefu wa upande wa mchemraba ($s$) ni 3 m.
Eneo la uso mmoja = $s^2 = (3 \text{ m})^2 = 9 \text{ m}^2$.

Mchemraba una nyuso 6.
Jumla ya eneo la nyuso = $6 \times \text{Eneo la uso mmoja}$
Jumla ya eneo la nyuso = $6 \times 9 \text{ m}^2 = 54 \text{ m}^2$.

Gharama ya kupaka rangi kwa kila mita ya mraba ni Ksh 150.
Jumla ya gharama = Jumla ya eneo la nyuso $\times$ Gharama kwa kila mita ya mraba
Jumla ya gharama = $54 \text{ m}^2 \times \text{Ksh } 150/\text{m}^2$
Jumla ya gharama = $\text{Ksh } 8100$.
Jumla ya gharama ya kupaka rangi mchemraba ni $\boxed{\text{Ksh 8100}}$.