Express x in terms of the other variables in the diagram below:

For the answer to the question above, just use similar triangles. 
Here's the equations that I used.

t/h = (x + t) / r 
x + t = rt / h 
x = rt / h - t 
I hope my answer helped you in your problem, Have a nice day

1. 0.3 •4 is the same as 4 groups of 0.32. 7•0.8 is the same as 7 groups of 0.83. it increases by 0.5 every time, so 0.5x4 it increases by 0.9 every time, so 0.9x5. 0.9•12=10.86. 0.47•5=2.35i can finish the next ones in a separate post

Ithink it's b sorry if i'm wrong