Western Rock Removal, Inc., agreed to work as a subcontractor on a sewer project on which Allegheny Water, Inc., was the general contractor.For drilling and blasting a certain amount of rock, Rock Removal was to be paid $29 per cubic yard or on a time-and-materials basis, whichever was less.From the beginning, Rock Removal experienced problems.The primary obstacle was a heavy concentration of water, which, according to the custom in the industry, Allegheny should have controlled but did not.Rock Removal was compelled to use more costly and time-consuming methods than anticipated, and it was unable to complete the work on time. The subcontractor asked Allegheny to pay for the rest of the project on a time-and-materials basis.Allegheny signed a modification of the original agreement.On completion of the work, Allegheny refused to pay Rock Removal the balance due under the modification.Rock Removal filed a suit in a Pennsylvania court against Allegheny.Allegheny claimed that the modification lacked consideration was thus not valid and enforceable.Is Allegheny right?Why or why not?