15. Kendrick also planted an oak tree in his front yard. He used landscape bricks to form a circular area around the tree which he will fill with mulch. The radius of the circle is \( 6 \) ft and he is filling it to a depth of \( 4 \) inches. The mulch he is buying comes in \( 2 \) ft \( 3 \) bags that cost \( \$ 3 \) per bag.
a. Convert \( 4 \) in to feet.
b. How much mulch does he need?
c. How many bags of mulch will he need?
d. How much will the mulch cost?