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