We have :
2 + .70x = ..75(x + 2) whhere x is the number of pounds of the 70% mix
Simplify
2 + .70x = .75x + 1.5 subtract 1.5, .70x from both sides
.5 = .05x divide both sides by .05
.5 / .05 = x = 10 lbs of the 70% mix
And (x + 2) = (10 + 2) = 12 lbs. total
