Question 618505
This is a proportion.

Let b be how fast a tourist can ride on is bicycle.

Then b-7 is how fast he can walk.

Recall that d = rt.

Then   33 = b*t  and  12 = (b-7)*t

We need to solve for b.

Since 12 = bt - 7t but recall that 33=bt so we have that:

12 = 33-7t

-21 = -7t

t = 3 hours.

33miles =  b* 3hours

b = 11 miles per hour.

That means b-7 = 4 miles per hour

Then following d =rt

30 = 4*t

30/4 = t

t = 7.5 hours

So he should allow himself 7.5 hours.