Question 893161
You should study the already-published lesson on this, but ...


u = grams of the cheap coffee
v = grams of the expensive coffee


{{{highlight_green((5u+9v)/16=7)}}} and {{{highlight_green(u+v=16)}}}.


The price-account equation is {{{5u+9v=7*16}}}
{{{5u+9v=112}}}


You have a system of the two linear equations:
{{{highlight_green(system(5u+9v=112,u+v=16))}}}
Choose whichever method you want, either substitution or elimination.