r – PCA –> Regression –> Prediction, how?

I have a data set of 81 cities and 44 variables and 4 dependent variables (Modal Split values, percentage of bike usage, car usage…).
I performed PCA on them, so I get 8 Principal Components.
After that, I did a multiple multivariate regression on them.
I am using R.

Now I want to input random data of another city, so I get a prediction.

The problem is my input data needs to be transformed first into the “PCA-form”, because the regression works with 8 principal components, where the data is transformed.

Can anybody help me?