I assume what you mean by this question is an equation like this:
1 + 2 x 3 + 4
Or,
3 x 4 + 6 /div 5
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What you'd do:
1+2 x 3+4 First, add either 1+2 or 3+4 which is 3 & 7. then, youd multiply your answers as, 3 x 7 which is, 21.
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Please ask if you have any questions