[sdiy] Newbie Electronics Math problem (I need help!)

[Sam Ecoff]

Hi All,

I'm attempting to solve a problem for my electronics class. I have the  
permission of the professor to ask for help, so here I am... I have  
put about an hour and a half into this, attempting to solve it myself,  
researching it on the internet, but I am stumped. The problem is from  
Page 41 of Electronic Technology Fundamentals 3rd ed. by Paynter and  
Boydell. It reads as follows:

18. The current through a wire is equal to 100mA. The energy being  
used by the voltage source is 2.5 x 10^-3 J. What is the value of the  
voltage source?

I understand that 1 Amp = 1 Coulomb per second, but given that they  
don't give an amount of time, that formula is not particularly  
helpful. I also get that 1V = 1Joule/Coulomb. I feel that without  
specifying a time period, the problem doesn't provide enough info to  
answer the question.

What am I missing here?

Sam E.