Please help, question in photo​

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.

Which ordered pair is the best estimate for the solution of the system of equations? the graph of the system of equations : y = 3/2x +6 and y=1/4x - 2 , -3) .5, -3.5) , -4) , -3.5)

40 points which is the equation of a line perpendicular to the line with the equation: y = 1/4x + 2 a : y = -4x - 7 b : y = 4x + 2 c : y = 1/4x - 1/2 d : y = -1/4x + 3