How to solve davis bought a second hand cycle for $500 he spent $80 in repairs and $175 in repainting he then sold it to john for $900 how much did he gain or lose?

So you would need to add:

500$ + 80$ + 175$ = 755$

Since John paid 900$ then you would subtract how much he is buying it for from how much Davis spent to fix it

900$ - 755$ = 145$ (on profit Davis earned)