How to solve this geometric progression? (finding the ultimate value)?

The question is; A plant is 50 cm high when it is first observed. One week later, it has grown 10 cm, and each week thereafter it grows 80% of the previous week's growth. Given that this pattern continues, what will be the plants' ultimate height? I got its ratio which is 1.80 The first term would be 50 cm right? The second one would be 60, but the third one would be 108 cm.. ...and this is kinda confuse. What does it means by ultimate height? Should we use sum to infinity formula? Thank you for solving this problem =D