Question 261881
LM + MN = LN by the segment addition postulate
So,
{{{7y + 9 +3y + 4 = 143}}}
combine like terms to get
{{{10y + 13 = 143}}}
subtract 13 to get
 {{{10y = 130}}}
divide to get
 {{{y = 13}}}
LM = 100
MN = 43