The answer is D. 14.2*0.784 We do not have to multiply these number to tell the number of decimal places of the product.
The product of a set of number will have the sum of the decimal places of the factors. For example, in
(A) 5.3478x6.4214 ⇒ 4+4= 8 decimal places
(B) 6.4x3.82 ⇒1+2= 3 decimal places
(C) 521x3.82 ⇒ 0+2 = 2 decimal places.
(D) 14.2x0.784 = 1+3= 4 decimal places