If 3t - 7= 5t, then 6t = what is the answer

Which addition property is being illustrated below? (type commutative or associative) (6 + 7) + 1 = 6 + (7 + 1)

Iwill give ! if m∠a=59 and m∠3=81°, what is m∠b? m∠b= _[blank]_°

Find the greatest common factor of the followig monomials 21u^5v,3u^4v^6, and 3u^2v^5