1. The problem statement, all variables and given/known data 6. If the exposure rate from 137Cs at one metre is 2.50 mGy/h, how many bequerels are present? 2. Relevant equations X=5.263 x 10-6 A∑(yiEi(μen/ρ)i)/r2 3. The attempt at a solution what im looking to do isnt to solve the question, i need to rearrange the formula above so that A is the subject and i have no idea where to begin due to its complexity. i would also like to know what the symbols represent, my interpretation from what i have found is that: X = the exposure measured in Roetengens A = The activity of the source measured in Bequerels ∑ = this sigma sign is equal to a complex value. To gather this number the individual energy of each photon that this radiation source can produce must be known and multiplied by the rate that they are produced. This is due to the fact that a gamma source does not produce a single energy level but instead there is a range of energies produced. yi = The initial Yield from this source before any decay Ei = the initial energy of this source before any decay E = the energy of the photons i = The value of i on its own refers to the fact that the calculation must use the initial values of μen/ρ. r^2 = the distance away that the measurement is taken please could someone check that this is correct. we were not given this formula or taught how to use it so im struggeling.