Question 1021055
He needs a volume of 
{{{V=5.5*6*(10/100)=3.33}}}{{{m^3}}}
So he needs,
{{{300*3.3=1000}}}{{{kg}}} cement
{{{600*3.3=2000}}}{{{kg}}} sand
{{{1200*3.3=4000}}}{{{kg}}} gravel
So the cost is,
{{{(1000/25)4.99=199.60}}} for cement.
He's already over budget.
{{{(2000/950)3.99=8.40}}} for sand.
{{{(4000/850)39.99=188.19}}} for gravel.
Totaled,
{{{T=199.60+8.40+188.19}}}
{{{T=396.19}}}