Ramp from irregular curve frame

Hi, I’m having trouble creating a slope with a 10% inclination, that connects a horizontal surface and another slope. The main issue is connecting the 2 surfaces (blue lines in the screenshot) with a slope whilst respecting the 10 % inclination, whilst it being properly horizontal.

Can anyone help me with a suggestion or stuff to try? I’m almost out of ideas, and what i tried didnt really work.