Ineed on 21- how to do it would be nice and if you could work one out and explain it that would be nice you

Triangles ABC and DEF are similar, which means corresponding sides occur in ratios with one another. Mathematically, this means

Also, corresponding angles are congruent. These are A and D, B and E, C and F.

As an example, for 21, the above equation turns into

and you can solve for and directly:

The others are solved exactly the same way. In each case, you happen to be given all the side lengths for one of the triangles, and one of the side lengths for the other triangle. So all you need to do is plug in what you know and solve for the remaining two sides.

3x + 18 = 147°

step-by-step explanation:

3x + 18 = 147°, because the value of the central angle is equal to the value of the arc formed by it.

i hope i you.