To find the estimated value of \( y \) when \( x = 170 \), you can substitute \( x \) into the equation of the trend line \( y = 1.1x + 15.8 \).
Substituting \( x = 170 \):
\[ y = 1.1(170) + 15.8 \]
Now calculate \( 1.1 \times 170 \):
\[ 1.1 \times 170 = 187 \]
Next, add 15.8 to this result:
\[ y = 187 + 15.8 = 202.8 \]
So, the estimated value of \( y \) when \( x = 170 \) is \( 202.8 \).
To the nearest tenth, the value is:
\[ \boxed{202.8} \]