7-15 ! i would really appreciate !

7. x=45 The angle is a right angle, which is 90 degrees. 45+45=90
8. x=45 3x+x=180>>  3(45)+45=180>> 135+45=180
9. x=30 2x+x=90>> 2(30)+30=90>> 60+30=90
10. x=50 2x+(x+30)=180>> 2(50)+(50+80)=180>> 100+(80)=180
11. x=30 (x+20)+(x+10)=90>> (30+20)+(30+10)=90>> 50+40=90
12. x=25 (x+20)+(5x+10)=180>> (25+20)+(5(25)+10)=180>> 45+(125+10)=180>> 45+135=180
13. x=9 6x+4x=90>> 6(9)+4(9)=90>> 54+36=90
14. x=34 (2x-10)+(3x+20)=180>> (2(34)-10)+(3(34)+20)=180>> (68-10)+(102+20)=180>> 58+122+180
15. x=18 (2x+15)+(3x-15)=90>> (2(18)+15)+(3(18)-15)=90>> (36+15)+(54-15)=90>> 51+39=90

C. expression because any expression or equation may contain more than one variable