Let D be the number of hours Doug spent in the tutoring lab, and let L be the number of hours Laura spent in the tutoring lab. Since Doug and Laura spent a combined total of 250 hours in the tutoring lab, the equation D+L=250 holds. The number of hours Doug spent in the lab is 40 more than the number of hours Laura spent in the lab, and so the equation D=L+40 holds. Substituting L+40 for D in D+L=250 gives (L+40)+L=250, or 40+2L=250. Solving this equation gives L=105. Therefore, Laura spent 4 hours in the tutoring lab.