Assume that the phone calls of the second evening is x
Since the phone calls of the third evening is two times the second,
Then the third evening is 2x
Since the first evening is 7 more than the second,
Then the first evening is x + 7
Since she received a total of 87 phone calls in the three evening
Add them and equate the answer by 87
[tex]x+7+x+2x=87[/tex]Add the like terms in the left side
[tex]4x+7=87[/tex]Subtract 7 from both sides
[tex]\begin{gathered} 4x-7-7=87-7 \\ 4x=80 \end{gathered}[/tex]Divide both sides by 4 to find x
[tex]\begin{gathered} \frac{4x}{4}=\frac{80}{4} \\ x=20 \end{gathered}[/tex]Since x represents the number of phone calls in the second evening, 2x represents the third evening, and x + 7 represents the first evening
So:
1st evening = 20 + 7 = 27 phone calls
2nd evening = 20 phone calls
3rd evening = 2 (20) = 40 phone calls