Problem
The sentence becomes one expression, (box - 2) x 6 + 12 / 3 = 160, with parentheses holding the order.
Turning the words straight into symbols, with parentheses, is exactly what a fifth grader practices: record the calculation faithfully before computing.
5.OA.A.2Convert To AlgebraThe whole sentence becomes the single expression (box - 2) x 6 + 12 / 3 = 160.
The words say the subtracting happens before the multiplying, and parentheses are what hold that order inside an expression.
Multiplying by 6 makes 6 equal groups of whatever came out of subtracting 2, not 6 groups of the mystery number alone.
The multiplied part and the 12 divided by 3 are joined by adding, and together those two pieces make the whole 160.
The piece 12 divided by 3 doesn't depend on the mystery number at all, so finish that small subproblem first. It equals 4.
Doing the easy, fixed chunk first shrinks the problem and lets the parentheses-and-order rules guide what to evaluate.
5.OA.A.1Identify SubproblemsUndoing the last step, 160 - 4 = 156 is what the (box - 2) x 6 part came to.
Subtraction is the inverse of addition; peeling the last step off first is the heart of working backwards.
5.OA.A.1Work BackwardsDividing undoes the times-6, so box - 2 = 156 divided by 6 = 26.
Division undoes multiplication, so we keep stripping operations off the answer in reverse order.
5.OA.A.1Work BackwardsAdding 2 back undoes the first subtraction, so the mystery number is 26 + 2 = 28.
Addition is the inverse of subtraction, and this is the last operation to undo, so it reveals the original number.
5.OA.A.1Work BackwardsWhen you know the final answer, peel the operations off in reverse with their opposites to walk back to the starting number.