Answer + which expression is equivalent to (3x^2 - 7)? a. (2x^2 - 11) - (x^2 + 4) b. (5x^2 - 6) - (2x^2 - 1) c. (10x^2 - 4) - (7x^2 + 3) d. (15x^2 + 8) - (18x^2 + 1)

The half-life of a certain material is 0.004 second. approximately how much of a 20-gram sample will be left after 0.016 second? a. 5 grams b. 16 grams c. 0.32 gram d. 1.25 grams