A+B=C
Say that A and B must equal 10. For A, you input calculations using other
formulas and get that A=6, so automatically B must equal 4. However, say that
as a constraint, B has to equal 7 or greater. How do you make that cell
change the value in order to impose this new constraint either using formulas
or another method but not changing the values manually?

(If B is 5 for example, we order 7. But if B is 8 we leave it at 8.)

Thanks