Hello from MrBillDoesMath!
Answer:
283 degrees
Discussion:
A circle has 360 diverges so summing up all the angles gives:
360 = (7y - 7) + (20y-11) + (4y + 6) => combine like terms
360 = (7y + 20y + 4y) + (-7 - 11 + 6) =>
360 = 31y - 12 => add 12 to both sides
372 = 31y =>
y = 372/31 = 12
measure arc ABC =
360 - measure arc (7y-7) =
360 - (7*12-7) =
360 - (77) = 283
Thank you,
MrB