7x300=7x 3 hundres because in 300 hundreds there is 3 hundreds.I know that didnt make sense.so basically just look at the front number number its 3 so 3 hundreds but if your working with thousands and the front number is 5 its 5 thousands.I hope this was helpful.
The value of cos B is 12/13
1/2x-7=1/3x-4,
1/2x-3=1/3x,
1/2x-1/3x=3
1/6x=3/1/6
Final answer x=18
I hope you understand and best wishes!!