$125 per hour
For every hour (x), it costs 125.
So, the equation is:
y=125x
Where x is the number of hours and y the total cost.
(x,y) = (0,0) , (1,125) are possible points of the function line. (0,0) means 0 cost for 0 hours and (1,125) means that for 1 hour, it costs $125.
For 12 hours:
y = 125(12) = $1500
If you spent $750:
750 =125x
Solve for x:
750/125 = x
x= 6 hours