A risk manager builds a two-factor model for a bond portfolio where the factors are the level and slope of the yield curve. The portfolio has a level factor sensitivity of -7.2 and a slope factor sensitivity of 3.1. The level factor has a standard deviation of 80 bps, the slope factor has a standard deviation of 45 bps, and their correlation is -0.35. What is the portfolio's factor-based volatility (in basis points)?