You know that 1 pound of coffe costs $7.81
Also the gift card had an initial amount of $90 and there where $58.76 left after her coffee purchase.
1 step: calculate how much she spent by subtracting the final amount to the initial one:
$90-$58.76= $31.24
2 step: using the price per pound calculate how many pounds she bought. You can use cross multiplication for this step:
$7.81_____1pound coffee
$31.24____xpounds coffee

Linda bought 4 pounds of coffee.