4. D
12/15 isn't the same as 30/40. 12/15=0.8, while 30/40=0.75. All the other options are equal.
5. C
Of course, you could figure this out by plugging in all the answers, and seeing which ones make the two sides equal, however, cross multiplying (multiplying the top of one fraction with the bottom of the other fraction) would be much faster. This will be your equation: 8*46=18*n. After combining like terms and dividing, you should find that n=20.
6. A
This problem is basically the same as #5. Cross multiplying so the equation you get will be 0.6*1.2=1.6*w. W should be 0.45.
Hope this helps!!
