Question 305448
Let your first number be A. 
Let the other number be B.
{{{A+B=58}}}
{{{B=A+17}}}
Substitute for B in the first equation and solve,
{{{A+(A+17)=58}}}
{{{2A=41}}}
{{{A=41/2}}}
{{{B=A+17}}}
{{{B=41/2+34/2=75/2}}}
Your first number is 41/2 and the second is 75/2.