What is the value of a?
6 ( a + 2 ) + 3 = 3 ( 10 - 3a )

6(a + 2) + 3 = 3(10 - 3a)

First, expand. / Your problem should look like: 
Second, add up 6a + 12 + 3 to get 6a + 15. / Your problem should look like: 
Third, subtract 15 from both sides. / Your problem should look like: 
Fourth, subtract 30 - 9a - 15 to get -9a + 15. / Your problem should look like: 
Fifth, add 9a to both sides. / Your problem should look like: 
Sixth, add 6a + 9a to get 15a. / Your problem should look like: 
Seventh, divide both sides by 15. / Your problem should look like: 

 a = 1

6(a+2)+3=3(10−3a)

(6)(a)+(6)(2)+3=(3)(10)+(3)(−3a)(Distribute)

6a+12+3=30+−9a

(6a)+(12+3)=−9a+30(Combine Like Terms)

6a+15=−9a+30

6a+15=−9a+30

Add 9a to both sides.

6a+15+9a=−9a+30+9a

15a+15=30

Subtract 15 from both sides.

15a+15−15=30−15

15a=15

Divide both sides by 15.

15a/15=15/15

a=1

40 & 50 in the right corner are the complementary angles as when placed in a sum (added together) they make 90°