A regular hexagon and a regular octagon are joined as shown on the diagram.

Work out the size of angle x.

x = 120°

Step-by-step explanation:

I think your question missed key information, allow me to add in and hope it will fit the orginal one. Please have a look at the attached photo,  

My

As we know the formula to calculate the measure of the interior angle in a regular polygon is equal to

where n is the total number of sides in a regular polygon.

In this question, n = 6 because it is a regular hexagon

=> the interior angle of it is;

From the picture you can see that, 1 interior angle of the 1st hexagon plus 1 interior angle of the 2nd hexagon plus x is equal to 360°

<=> 120° +120° + x = 360°

<=> x = 120°

Hope it can find you well.