How long must $542 be invested at a rate of 7% to earn $303.52 in interest

The number of years that must be invested at  a rate of 7 % to earn$ 303.52 in interest is

    8 years

 calculation

                   P  is the principal   money to be invested =  $ 542

                       r= rate= 7/100=0.07

                      t=  time required

=$ 845.52=$ 542( 1+  0.07 t)

    =$  845.53 -$542  = $37.94 t

   =$303.52 =$37.94 t

  =  $303.52/ $   37.94  =  $37.94t/$37.94

  t=  8 years

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.