The LCM of 28, 60, 120 and 135 is:

$28 = 2^2 \times 7$
$60 = 2^2 \times 3 \times 5$
$120 = 2^3 \times 3 \times 5$
$135 = 3^3 \times 5$
Highest powers:
$2^3, 3^3, 5, 7$
LCM = $ 2^3 \times 3^3 \times 5 \times 7$
$= 8 \times 27 \times 5 \times 7$
Answer = 7560