Answer
LCD is 140.
Work Step by Step
To find the least common denominator factor each denominator then multiply each factor the greatest number of times it occurs in either number.
$4=\underline2\times\underline2$
$14=2\times\underline7$
$20=2\times2\times\underline5$
$LCD=2\times2\times7\times5=4\times35=140$