Answer:
I can not give an exact solution, because I can not draw in the given image and I don't know the scale of the image, but I can give a general way of solving this.
We know that a circle is a shape such that al the points are equidistant to the center.
So, if Bertie is always exactly 1.3cm from crumb A, then all the possible positions of Bertie are shown by a circle of radius = 1.3cm around crumb A.
And if Adam is always exactly 3.5cm away from crumb B, then the possible positions of Adam are shown by a circle of radius = 3.5cm around crumb B.
So to solve this problem, you need to draw these two circles, and the points where the circles intersect each other will be the points where Bertie and Adam could meet.