To find the surface area of a rectangular prism, we use the formula:
\[ \text{Surface Area} = 2(lw + lh + wh) \]
where:
- \( l \) is the length,
- \( w \) is the width,
- \( h \) is the height.
In this case:
- Length (\( l \)) = 12 inches
- Width (\( w \)) = 5 inches
- Height (\( h \)) = 3 inches
Now, we will substitute these values into the formula:
- Calculate \( lw \):
\[ lw = 12 \times 5 = 60 \]
- Calculate \( lh \):
\[ lh = 12 \times 3 = 36 \]
- Calculate \( wh \):
\[ wh = 5 \times 3 = 15 \]
Now we can add these values together:
\[ lw + lh + wh = 60 + 36 + 15 = 111 \]
Now, we multiply by 2:
\[ \text{Surface Area} = 2 \times 111 = 222 \]
Thus, the surface area of the rectangular prism is:
\[ \boxed{222 \text{ square inches}} \]