Table: german_grand_prix_1987
Columns: driver
constructor
laps
time_retired
grid

Question: How many laps are associated with a time of + 1:39.591?
SQL: SELECT "laps" FROM german_grand_prix_1987 WHERE "time_retired" = '+ 1:39.591'

Question: What is the average number of laps for a grid of 6?
SQL: SELECT AVG("laps") FROM german_grand_prix_1987 WHERE "grid" = 6