The sum of two numbers is 35. the smaller number is 5 less than the larger number. what are the numbers?

If large number = a
and small number = b

so
a + b = 35
and
b = a - 5
subtitute b to the first equation
a + (a - 5) = 35
2a - 5 = 35
a = (35 + 5)/2
a = 20

substitute a
a + b = 35
20 + b = 35
b = 35 - 20
b = 15
&2as