Question

find m(angle) ABC

21

132

48

19

Answer 1

I don't like these algebra problems which pretend to be geometry.

These are supplementary angles adding to 180 degrees; geometry done.

7x - 1  + 3x - 9 = 180

10 x = 190

x = 19

ABC=3x - 9 = 3(19) - 9 = 48

Answer 48°

Answer 2

m<ABC and m<ABD are supplementary angles and as you know sum of supplementary angles = 180°

so m<ABC + m<ABD =  180°

3x - 9 + 7x - 1 = 180

Combine like terms

10x - 10 = 180

Add 10 to both sides

10x = 190

Divide both sides by 10

x = 19

Plug in x = 19 into 3x - 9 to find m<ABC

m<ABC = 3x - 9 = 3(19) - 9 = 57 - 9 = 48

Answer

m<ABC  = 48°