Answer: Payback rule
Explanation: As per the pay back rule, the project which earns its initial investment more quickly is considered to be acceptable and profitable.
In the given case, the company is expecting a project which do not affect liquidity and does not take too much cost on research for the coming future. Thus, a project with a shorter time period of recovery of initial investment will be suitable fro them.
Hence the company should use payback rule to evaluate its product.