Find the cross-strata dip,
given trend+plunge and strike

Enter values, then press

Azimuth difference
(btwn strike & trend), θ
Plunge (ie., dip) of lineation, φ

The dip of cross-strata can be found using the plunge & trend (a.k.a. dip and dip direction) of an exposed cross-strata lineation (eg., at the blue arrow) on the erosion surface, plus the strike (direction) of a cross-stratum (green arrow).

cross-strata dip = arctan  tan(φ)
sin(θ)

Spreadsheet version (eg., for phone)