Let x gallons be the amount of pure antifreeze that should be added to the 30% solution to produce a solution that is 65% antifreeze. Then the total amount of antifreeze solution will be x+3 gallons.
There are 30% of pure antifreeze in 3 gallons of solution, then
3 gallons - 100%,
a gallons - 30%,
where a gallons is the amount of pure antifreeze in given solution.
Mathematically,

Now in new solution there will be x+0.9 gallons of pure antefreeze.
x+3 gallons - 100%,
x+0.9 - 65%
or

Answer: he should add 3 gallons of pure antifreeze.
Marcario should use 4 pounds of macadamia nuts and 8 pounds of almonds.
Explanation
given
cost of macadamia nuts per pound=$9
cost of almond nuts per pound=$5.25
cost of the mixture per pound=$6.5
total pounds of the mixture to be made=12
let the pounds of macadamia nuts=x
pounds of almond nuts=y
total pounds of nuts=x+y=12

solving (1) and (2)
x=4
y=8
ANSWER
a) One Solution
b) the solution is x=2
EXPLANATION
The given equation is:

We expand to get;

Group similar terms;

This implies that,

Divide both sides by 10 to obtain,

440- 2x= 244 // simplify the equation given