Answer:
75
Step-by-step explanation:
Let n stand-in for "number"
"If 13 is added to a number," so: n + 13
"and the sum is multiplied by three," so: 3(n+13)
"The result is," so: 3(n+13) =
"7 times the number decreased by 9," so: 3(n+13) = 7n - 9
Now you can simply by moving numbers across the equal sign:
3n + 39 = 7n - 9
39 = 4n - 9 (take 3n off from both sides)
48 = 4n (add 9 onto both sides)
12 = n
And then check:
3(12 + 13) = 7(12) - 9
3 x 25 = 7 x 12 - 9
75 = 84 - 9
84 - 9 = 75
