Tentukan nilai x, jika (2x + 1) + (2x2) + (2x + 3) + + (2x + 50) = 4.275

We have 50 groupings of parentheses. We can tell because the first parentheses has a +1 and the last parentheses has a +50.
50 * 2x = 100x
Now we have to find 1 + 2 + 3 + ... + 50.
Add 1 and 50 together. Now add 2 and 49 together. Add 3 and 48 together. Notice how each pair sums to 51. We have 50/2 = 25 pairs and each pair equals 51.
25*51 = 1275
100x + 1,275 = 4,275
100x = 3000
x = 30

B, 0.4 repeats so it is rational and square root of 16 is 4 so that is rational as well.