Create an instruction of type sideslope - use the intersect material layer and select finish grade and then for the ut slope enter the slope using node to node method and set node 1 to be the point at centerline at base of subgrade and use point 3 as the second point - use point 3 as the attachment point. You will probably need to change the setting called honor sign of tie slope to yes (project settings and computations, corridors- this will mean that you have to now key in fill slopes as a negative number (downwards is negative, upwards is positive) but then a cut or fill slope can be positive or negative which when using it in this situation may happen if the pavement is super elevated in any way (then the cross slope goes positive and negative
The alternative is to use a slope/slope but you can only do it if you have the nodes at the top and base of the slope you want to intersect - either in the model because of instructions or because you added them as reference lines to the corridor - then you pick point 3 as the reference point, for the first slope you pick the 2 points at the base of the subgrade and for the second ref point use the top of the slope and then use the slope between the top and bottom of the slope- add the reference lines by editing the corridor itself (not the template) and add the 3d lines that make up the surface - they will then show up in the template editor as nodes that you can use to add instructions to / from / with etc.
Hope this helps
Alan