Question 1200089
Routine, been done many times in different examples.


pepper cheddar  $13 per kg
penn jack $9 per kg
want mix of 5 kg costing  $10.2 per kilogram


If use unknown w kg of pepper cheddar then  {{{13w+9(5-w)=(10.2)(5)}}}; and you can simplify and solve for w.  Hold off on all computations until last.