Answer:
The sum of three integers is 280.
a + b + c = 280
;
The sum of the first and second integers exceeds the third by 70.
a + b = c + 70
:
the third integer is 21 less than the first.
c = a - 21
:
Rearrange the 2nd equation and use elimination with the 1st equation
a + b + c = 280
a + b - c = 70
------------------subtraction eliminates a & b, find c
0 + 0 + 2c = 210
c = 210/2
c = 105
then
105 = a - 21
a = 105 + 21
a = 126
Find b using the 1st equation
126 + b + 105 = 280
b = 280 - 231
b = 49
:
:
See if that checks out
126 + 49 + 105 = 280
:
the three integers. 126, 49, 105
