Question 553425
First we factor {{{14y^2+42y))) and {{{7y^2+35y+42}}}
{{{14y^2+42y=14y(y+3)}}}
{{{7y^2+35y+42=7(y^2+5y+6)=7(y+3)(y+2)}}}
Both expressions have {{{7}}} and {{{y+3}}} as a common factor, so that will help.
{{{14y(y+3)(y+2)=14y(y^2+5y+6)=14y^3+70y+84}}} is the least common multiple, made by multiplying all the factors present in one and/or the other expression.