If someone could me with this that would be great

Prove
 m∠5+m∠2+m∠6=180°

we have that
m∠1+m∠2+m∠3=180°   equation I

m∠1=m∠5  > internal alternate angles  equation 2

and

m∠6=m∠3 > internal alternate angles    equation 3

I substitute  equation 2 and equation 3 in equation I

m∠1+m∠2+m∠3=180° > m∠5+m∠2+m∠6=180° > is ok

)because it's going in order of the math sign