What you need to know for this case is that the sum of the internal angles of a triangle is 180 °
We then have the following equation that is given by:
(2x) + (3x) + (4x) = 180
Clearing x we have:
9x = 180
x = 180/9
x = 20
Therefore we have:
m∠A = (40) °
m∠B = (60) °
m∠C = (80) °
Answer:
B) m∠B = 60 °
He practiced for 1 hour and 30 minutes
