Stephen evaluated (6.34 x 10^-7)(4.5 x 10^3). his work is shown below. which statements describe his errors? check all that apply. (6.34 x 10^-7)(4.5 x 10^3) (6.34 x 4.5)(10^-7 x 10^3) 28.53 x 10^-4 -28.53 x 10^4 -2.853 x 10^3 a. he changed the sign of the coefficient. a negative exponent does not affect the sign of a coefficient in scientific notation. the sign of the exponent determines the direction the decimal is moved in. b. he rewrote -28.53 x 10^4 incorrectly; 28.53 x 10^4 = 2.853 x 10^5. the exponent is increased to account for the extra place the decimal is moved. c. he did not correctly evaluate the exponent. it should be evaluated as (10^-7 x 10^3) = 10^3 since exponents are evaluated using the same operation as the coefficients. d. he got the wrong value for the coefficients; 28.53 x 10^-4 is not possible. the coefficients in scientific notation are always greater than 1, but less than 10. f. he multiplied the coefficients; he should have added 6.34 and 4.5. the product of powers rule states that coefficients are added. keep in mind that there is multiple answers.