$Apple\ muffin\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Bran\ muffin\\10\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 4\\15\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 6\\20\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 8\\35\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 14$

Step-by-step explanation:

$For\ 5\ apple\ muffins, bran\ muffin=2\\\\Ratio\ of\ bran\ muffin\ to\ apple\ muffin=\frac{number\ of\ bran\ muffin}{number\ of\ apple\ muffin}\\\\Ratio\ of\ bran\ muffin\ to\ apple\ muffin=\frac{2}{5}\\\\Bran\ muffin=\frac{2}{5}\times apple\ muffin\\\\When\ apple\ muffin=10\\\\Bran\ muffin=\frac{2}{5}\times 10=4\\\\When\ apple\ muffin=15\\\\Bran\ muffin=\frac{2}{5}\times 15=6\\\\When\ apple\ muffin=20\\\\Bran\ muffin=\frac{2}{5}\times 20=8$