How can you find the surface area of a composite solid made up of prisms ? ()

Oh, this is easy. For any prism, you find the surface area by finding the are of all the sides. I will post all surface area formulas here, for reference
Cube:

Surface area = 6 × a2

Right circular cylinder:

Surface area = 2 × pi × r2   +  2 × pi × r × h

pi = 3.14
h is the height
r is the radius

Rectangular prism:

Surface area = 2 × l × w  +  2 × l × h  +  2 × w × h 

l is the length
w is the width
h is the height

Sphere:

Surface area = 4 × pi × r2 

pi = 3.14
r is the radius

Right circular cone:

Surface area = pi × r2  +  pi × r ×( √(h2 + r2)) 

pi = 3.14
r is the radius
h is the height
l is the slant height 

Right square pyramid:

Surface area = s2 + 2 × s × l

s is the length of the base
h is the height
l is the slant height