I am writing a paper on how racial attitudes affect voting for authoritarian populist parties. In my analysis I want to include an index for racial attitudes. This index includes 3 variables (immigration is good for economy, immigration is good for cultural life, immigrants make country a better place to live). These variables are all scaled from 1-10 points. Now I want to create the index by summing these items and standardizing them to a 0-100 point scale for ease of interpretation. I am, however, unsure on how to do this in SPSS. I would be very grateful for any tips on how to do this. Thank you!