Question 4860
Let T = The number of T-shirts bobby sold
Let S = the number of socks bobby sold

9T = The total dollars that the T-shirts earned
5S = The total dollars that the socks earned

We know that the total sales from both came to $287, So:

9T+5S=287

And we know that he only sold a total of 35 items:
T+S=35

This can be rewritten as S=35-T, by subtracting T from both sides.

Then used 35-T to put into our total sales equation as a substitution for S:

9T+5(35-T)=287

Clear the parentheses:
9T+175-5T=287

Combine like terms (subtract $175 from both sides of the equation)

4T=112

Divide both sides by 4

T=28 

He sold 28 T-shirt, so he sold 7 pairs of socks (35-28=7)

Check your answer:

28*9.00=$252
7*5.00= $ 35

252+35=287, so this is correct.