Question 119880
Let x represent the number of days.
The cost of the first bulb would be 
0.50+0.12x 
and the second would be 
2.50+0.02
Since they need to be equal set up would look like this
0.50+0.12x = 2.50+0.02x
now solve for x
0.50+0.12x = 2.50+0.02x
0.12x-0.02x = 2.50-0.50
0.10x = 2.00
x = 20 days
Now to find the amount replace x with 20
0.50+0.12(20) = 2.50+0.02(20)
$2.90 = $2.90