How many subshells are in the n = 4 shell?

The number of subshells in any given shell is equal to that shell's number. So the first shell (n=1) contains 1 subshell (1s). The second shell (n=2) contains 2 subshells (2s and 2p). The third shell (n=3) contains 3 subshells (3s, 3p, and 3d), and the fourth shell (n=4) contains 4 subshells (4s, 4p, 4d, and 4f).

All d-type subshells have 5 orbitals, regardless of which shell they're in. s-type subshells contain 1 orbital each, p-type subshells contain 3 orbitals each, and f-type subshells contain 7 orbitals each. The answer would still be "five" even if you'd said 3d, 4d, or 6d ... they all have five orbitals.