3. The Philippine Airlines (PAL) and the Chamber of Real Estate Builders Association (CREBA) filed a Petition to the Supreme Court questioning the validity of Republic Act No. 7716 (An Act Restructuring the Value Added Tax System Widening Its Tax Base and Enhancing Its Administration) because it impairs obligations of contracts on existing sales on real property payable in installments, franchise privileges, and exempt transactions such as the sale of agricultural products, food items, petroleum, and medical and veterinary services. Is the contention of PAL and CREBA correct? Explain with legal basis.