13. One type of granola has $30 \%$ nuts, by mass. A second type of granola has $15 \%$ nuts. What mass of each type needs to be mixed to make $600 \mathrm{~g}$ of granola that will have $21 \%$ nuts?

Step 1 ：Let's denote the mass of the first type of granola as x and the mass of the second type as y.

Step 2 ：We know that the total mass of the granola mix is 600g, so we can write the equation as \(x + y = 600\).

Step 3 ：The total mass of the nuts in the mix is 21% of the total mass, so we can write the equation as \(0.3x + 0.15y = 0.21 \times 600\).

Step 4 ：We can solve this system of equations to find the values of x and y.

Step 5 ：The solution to the system of equations is \(x = 240\) and \(y = 360\).

Step 6 ：The mass of the first type of granola that needs to be mixed is \(\boxed{240 \mathrm{~g}}\) and the mass of the second type of granola that needs to be mixed is \(\boxed{360 \mathrm{~g}}\).