S=180n-360 for n solve for n

Which of the fallowing best completes the sequence 12,8,5, a) 1 b) 2 c)4 d)0

Isabelle is mixing red and blue paint to make purple paint she adds 3/10 of a fluid ounce of red to 12/25 of a fluid ounce of blue to make 1 1/30 fluid ounces of purple how many fluid ounces of red paint ounces of red paint will she need to make 3 fluid ounces of purple paint

Could you show the work on how u got this so i could understand?