Question 730310
Someone/something needs M gallons of mixture containing T% component. how many gallons each of material containing H% component and material containing L% component must be used to obtain the desired M gallons? 


Letting u = gallons of the L% component material and v = gallons of the H% component material,


{{{highlight((Lu+Hv)/M=T)}}} and {{{highlight(u+v=M)}}}.
That is the general system.  Solve for u and v.  You can solve in general for this and general situations like this, and then substitute the values needed for any specific situation.