What can be used to explain a statement in a geographic proof

#12 find the value of x. #13 find the value of the variable.

Can someone check if i did this correct. it’s number 4 if you’re wondering.

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