Okay, time for the new puzzler. This one is not that great, but it is what we have. Might be the worst one. But it is what we have. 

So, here we go.

A while back, we were driving in the mountains, down those long twisty mountain passes. And while were driving there, we saw signs that said, "Caution. 6% grade next three miles. Trucks use low gear."

Now, they must consider a 6% grade to be a serious grade for a motor vehicle. And the way a grade is defined is this. On a 6% grade, the elevation drops or rises six feet vertically for every 100 feet of road. So if you were driving horizontally for 100 feet, you would have gone up or down by six feet.

I know that doesn't seem like much. But if you think about it, 60 miles per hour means you're going 88 feet per second. So if we round up to 100, at a 6% grade, that means you are dropping 6 feet, every second or so, if you're going about 60 miles per hour. When you put it that way, it does seem like a lot. 

So, knowing this information, what would you guess is the steepest grade and percent of a drivable street in the city of San Francisco?

The city of San Francisco has some of the steepest streets that we know of. 

So, the question is, what's the steepest grade of a drivable street in the city of San Francisco? 

And for extra credit, what is the name of the steepest street?