confused on backspacing

71DodgeDemon340 said

Also dont forget if your shooting for 4.5 bs on the rear and find wheels with 5.5 bs you can use a one inch spacer to get the bs you want.

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I found wheels with 4.5 backspacing will that also work up front. The wheel that was on there before has a backspacing of 3.75 and its width is 7", will a 8" with 4.5 work up front