Answer
(a) $36$
(b) $360$
(c) $98000$
Work Step by Step
(a) Factor each number: $12=2\cdot2\cdot3$ and $18=2\cdot3\cdot3$
Thus $lcm(12,18)=2\cdot2\cdot3\cdot3=36$
(b) Each number have been factorized:
Thus $lcm=2^3\cdot3^2\cdot5=360$
(c) Factor each number: $2800=2^4\cdot5^2\cdot7$ and $6125=5^3\cdot7^2$
Thus $lcm(2800,6125)=2^4\cdot5^3\cdot7^2=98000$