Verified Answer :

AL2006

It's about 172 degrees.

\(Perimeter\ of\ the\ circle:L=2\pi r;\ r=7\\\\L=2\pi\cdot7=14\pi\approx14\cdot3.14=43.96\\\\\dfrac{21}{43.96}\approx0.477707\\\\0.477707\cdot360^o\approx171.97^o\approx172^o\\\\Answer:\boxed{172^o}\)