Draw a symmetrical thingy, the calculations are then simple. I'll let you figure out on your own what calculation is connected with what geometry:

sqrt(24^2+7^2) = 25

25 + 7 = 32

sqrt(32^2+24^2)=40

40/2=20

x = sqrt(25^2-20^2)=15

Have a look at loops.video, I think the ambition is for it to be an Activity Pub tiktok clone