:7. The class intervals of the histogram shown in figure ? on
page ? of the test has class intervals 0 - 1, 1 - 2, and 2 - 4. 
The block over 2 - 4 is missing.  How tall should it be? <p>

a.  10
 b.  20
 c.  30
 d.  40
 e.  50 <p>