On these questions. show work it would a lot. : )

10: an isosceles base angles are both equal. A triangle has 3 angles. All three angles added equals 180 in every triangle. since one of the base angle is 72 degrees then the other base angle is 72 degrees. ( a triangle has two base angles).  so 72+72= 144
                                          
                                           180-144= 36
The vertex angle = 36 degrees.

11: angles ratio is 2:4:6. Remember that all angles equal 180. Add the ratio amounts, 2+4+6= 12.  Then divide 180 by 12 (180/12 = 15).
 the smallest angle ratio is 2, so multiply 15 by 2 ( 15 * 2= 30 )
the smallest angle is 30 degrees.

12: all three angles of a triangle adds up to 180. thus, 64 + 74 + x = 180
                                                                                           138 + x = 180
                                                                                             x= 180 - 138
                                                                                             x = 42
x is the third angle. so the third angle is 42 degrees.