During the week, edward spent $90. at the end of the week, he had $45 remaining. how much money did he have at the beginning of the week?

During the week Edward spent $90 (-90 from total amount). He has $45 remaining. Let x be the amount he started with

x - 90 = 45    is your equation.

To solve for x, isolate it. Note the equal sign. What you do to one side, you do to the other. Add 90 to both sides

x - 90 (+90) = 45 (+90)

x = 45 + 90

Simplify

x = 135

$135 is the amount Edward started out with in the beginning of the week.

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