numbers first:
lcm of 15, 5, and 6 is 30
next the c's
lcm of c^2, c^6, and c^7 is c^7
note: c^7 = c^2 * c^5 and c^7 = c^6 * c
next the b's
the lcm of b^6, b^4, and b^3 is b^6
the lcm for the whole thing is 30(c^7)(b^6)
note: you don't have to write it with parentheses. there's no easy way to do exponents on this page, so I wrote it with parentheses here.