So, Bob needs 2 cups of concentrate (I'll use the variable c to shorten it) for every 3.5 cups of water (w). When he has 6 cups of c, he has three times the original recipe, and therefore we need 3w as well.
3.5x2=6+1=7. So we need 7 cups of water.
Now, 6 cups of concentrate + 7 cups of water = 13 cups of orange juice.
All angles in a triangle add up to 180 so 180 - 60 = 120 then 180 - 155 = 25 then 25+65 = 90 that is the remaining angle but finally 180 - 90 = 90 is the missing angle