its a algebra word problem
Here again choose a variable for the unknown, what problem is asking you to find out.
X - amount of $9.00/ lb need to be mixed with $5.00/ lb
X ( 9.00) + 5( 50) = ( X + 50) (6.50) to mixing means adding up the weights .
9X + 250 = X ( 6.50) + 325
9X - 6.50 X = 325 - 250
2.50 X = 75
X = 75/ 2.50 = 30 lb