1. The quadrilateral ABCD is inscribed in circle O, then, the sum of its opposite angles is 180°.
2. As you can see, m∠A=2x-7 and m∠C=x+4 are opposite angles, then, you have:
m∠A+m∠C=180°
3. When you substitute the values of m∠A and m∠C into m∠A+m∠C=180°, you obtain:
m∠A+m∠C=180°
(2x-7)+(x+4)=180°
4. You must clear the "x", as below:
3x-3=180°
3x=180°-3
x=177°/3
x=59°
5. Now, you can substitute the value of "x" into m∠B=2x+3:
m∠B=2x+3
m∠B=2(59°)+3
m∠B=118°+3
m∠B=121°
What is m∠B ?
The answer is: m∠B=121°
