I assume you mean
2 tonnes of sand at £75.00 per tonne
20 bags of cement at £6.70 per bag
350 bricks at 45p each
If so, then
2 tonnes of sand at £75.00 per tonne = 2 * £75.00 = £150.00
20 bags of cement at £6.70 per bag = 20 * £6.70 = £134.00
350 bricks at 45p each = 350 * £0.45 = £157.50
Add the three amounts
£150.00 + £134.00 + £157.50 = £441.50
Answer: 441.50