To find out how many trips Farid needs to make to walk a total of 20 kilometers, we can use the equation provided:
\[ d = t + 6 \]
We want to find the value of \(t\) when \(d = 20\). So, we can set up the equation:
\[ 20 = t + 6 \]
Next, we will solve for \(t\).
First, subtract 6 from both sides:
\[ 20 - 6 = t \]
\[ t = 14 \]
Therefore, Farid will have to make 14 trips to walk a total of 20 kilometers.