9x^2 + 6y

Replace x

9 * (5)^2 + 6y

9 * 25 + 6y

225 + 6y

Replace y

225 + 6*(3)

225 + 18

243

======================

x^2 / 2z + y

Replace x

3^2 / 2z +y

9 / 2z + y

Replace z

9 / 2*(-5) + y

9 / -10 + y

Replace y

9/ -10 - 1
9/-11

-9/11

====================================

z^2/-2x + y

Replace z

(-1)^2 / -2x + y

1/-2x + y

Replace x

1/-2*(-5) + y

1/10+y

Replace y

1/ 10-4

1/6

===================

P = 2(L+W)

Replace both L and W

P = 2(12+3)

P = 2(15)

P = 30

==================

17v^2+12v+3(v^2-4v)-5v(-4v+12)

Expand 3(v^2-4v)

3(v^2-4v) = 3v^2 - 12v

Expand -5v(-4v+12)

-5v(-4v+12) = 20v^2 - 60v

Now we have

17v^2 +12v+ 3v^2 -12v+ 20v^2 -60v

Group by similar

17v^2 + 3v^2 + 20v^2 +12v-12v-60v

and we just add

40v^2 -60v