Find two numbers, if their sum is −7 and their difference is 14

Let
a> first number
b> second number

we know that
a+b=-7> a=-7-b> equation 1
a-b=14> equation 2

I substitute 1  in 2

(-7-b)-b=14> -7-b-b=14> -7-2b=14> 2b=-7-14
2b=-21> b=-10.5
a=-7-b> a=-7-(-10.5)> a=-7+10.5> a=3.5

the answer is
the two numbers are 
a=3.5
and
b=-10.5

The first one is 2/3the second is 1/160the third is 4/125