Question 807978
This same exercise problem occurs very frequently, shown in many different examples.


ASSIGN VARIABLES
L = 5% alcohol
T = 30%, the concentration target
H = 95%, the high concentration material
M = 810 mL, amount of T conc. wanted
u = unknown amount of L material
v = unknown amount of H material


FORMULATE EQUATIONS

{{{highlight((Lu+Hv)/M=T)}}} and {{{highlight(u+v=M)}}}


SOLVE THE SYSTEM FOR u AND v.
You do the steps.  The essential part (or maybe half of it) was to form the system of equations.  The steps after that are routine.