Question 725241
Two equations would be needed.  One to account for money and the other to account for mass.


x = pounds of $5.20/pound coffee
y = pounds of $6.30/pound coffee


{{{5.20x+6.30y=170}}}.  That accounts for the money but uses two variables.


The grocer wants a mixture of 30 pounds of coffee, so 
{{{x+y=30}}}.


Two equations in two unknowns.  Solve for x and y.