If the world’s population is increasing at an annual rate of 1.3%, and there were 5 billion people in the year 1986, then in what year will the world’s population be 10 billion?

5 billion * ( 1 + 0.013 ) ^x = 10 billion
1.013 ^x = 10 : 5 = 2

x = 54
1986 + 54 = 2040
In the year 2040 the world`s population will be 10 billion. 
 

The answer is 40 degrees. angle x and angle y form vertical angles, therefore x = y. angle y forms a straight line with the 80° angle and the 60° angle which means that 80° + 60° + y = 180°. 140° + y = 180°. y = 180° - 140°. y = 40°. as mentioned earlier: x = y, so x = y = 40°.i hope that my answer is ! let me know if you need something more : )