need help with this math question, explanation will be greatly appreciated

Q1. Consider the following options for characters in setting a password:

• Digits = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }
• Letters = { a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z }
• Special characters = { *, &, $, # }

Compute the number of passwords possible that satisfy these conditions:

• Password must be of length 7.
• Characters can be special characters, digits, or letters.
• Characters may be repeated.