In this Teen Astronomy Cafe — To Go! Instant Pack students will explore the astronomical phenomenon of gravitational lensing. Students will use models to explore techniques astronomers use to determine the mass of a galaxy by examining the lensing effects. Students will understand and predict the effects of changing the physical properties of a lensed and lensing galaxy. This activity is conducted in a Python Notebook, a web-based interactive computational environment that contains code, text, and plots.