How much sand do you need to add to 4 m³ of soil with 50% sand in order to make soil with 80% sand?

6m^3

Step-by-step explanation:

Again with the buckets.

50+100=80

04+  x  =4+x

200+100x=320+80x

20x=120

x=6

u = -(6/7)w

step-by-step explanation:

place all values with 'u' on one side of the equation.

4u + 8w = - 3u + 2w

4u + 3u = 2w - 8w

further simplify the equation by solving the addition and subtraction.

7u = - 6w

make 'u' the independent variable by placing its co-efficient on the right-hand side.

u = - (6/7)w