Finding Weeks for Equal Savings

John and Lisa are saving money to buy a laptop. John saves $7 each week and has already saved $28. Lisa saves $4 each week and has saved $12 so far.

Let $J$ represent the total amount of money John will save after $w$ weeks, and let $L$ represent the total amount Lisa will save after $w$ weeks. The equations representing their savings are:

$J = 7w + 28$

$L = 4w + 12$

Determine the number of weeks $w$ it will take for John and Lisa to have saved the same amount of money. Enter your answer as a decimal or a fraction (e.g., 2 or 2/5).