help needed please

from the line segment,
MP = MN + NP
because before you can reach MP on the line segment, you first need to get to MN and then NP , which is equal to moving directly from M to P
and from the line segment,
MP = 5y +9
MN = 17
NP = 3y
substitute them in the equation
MP = MN + NP
5y +9 = 17 + 3y
group like terms
5y - 3y = 17 -9
2y = 8
dividing through by 2
2y/2 = 8/2
y = 4
but the question said we should find MP
which is equal to 5y + 9 on the line segment
but y = 4
MP = 5(4) + 9
MP =20+9
MP =29