Use the reciprocal property to solve for x : 3/540= 10/x

Need on this one asap im almost done with this subject

Plzz ! if you were constructing a triangular frame, and you had wood in the length of 4 inches, 4 inches, and 7 inches, would it make a triangle? would you be able to create a frame from these pieces of wood? yes or no? = explain your mathematical thinking/show your work:

5cakes cost 3.50 how much do 7 cakes cost