Answer:
Portfolio´s beta: 1.16
Explanation:
Stock     Percent     Beta Weighted Beta
 X           36%      1,19          0,43
 Y           18%     0,87      0,16
 Z           46%      1,26      0,58
                           1,16
The portfolio beta is obtained by the sum of the individual betas of each stock considering it´s  percent on the portfolio (weighted beta).
It represents the relative volatility of a portfolio relative to the market. More than one means more volatile and less than one means less volatile than the market.