Or use trig to find the angle, the heading required is 196 degrees.

First, square the dimensions of the two known sides

20*20 = 400
70*70 = 4900

They total 5300, take the square root of that to get 72.8 nm between the two points.

Now, divide 20/72.8 and use a calculator to find the sin -1 of the resulting dividend, which is rounded to 16 degrees. Add 16 degrees to 180 degrees to find the necessary course change to reach the 180/70.

Easy, peasy

GF