The amount you desire, 30,000 is double (2 times) the amount you have, 15,000.
If r is the annual interest rate, the annual multiplier is (1+r). After 4 years, you want the multiplier to be 2, so the relationship is
... 2 = (1+r)⁴
... r = 2^(1/4) - 1 . . . . solve for r
... r ≈ 0.1892 = 18.92% . . . . matches selection d.
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You can estimate this using the "rule of 72", which says the product of interest rate and doubling time (years) is about 72. That is, the rate will be about 72/4 = 18 percent.
