The table shows how the cost of a tractor repair depends on the time needed for the repair.
 Repair time Cost 
 (hours ) (dollars)
ーーーーーーーーーー
 2 I 180
 5 I 450
 ? I 630
 10 I 900 
 20 I 1,800
Which expression can be used to find the number that is missing from the third row of the table?
A. 450➗5
B. 630➗7
C. 450➗90
D. 630➗90