Why does pople now that there is 200 and they use 190 how many is left

Asystem of equation is shown below 6x - 2y equals 3 . and 5x + 3y equals 4. would you solve by substitution or elimination? and why

If you answer right ill give brainliest, : )

A33 gram sample of a substance that's used to detect explosives has a k-value of 0.1473. n = noekt no = initial mass (at time t = 0) n = mass at time t k = a positive constant that depends on the substance itself and on the units used to measure time t = time, in days