4 August to 4 September is 28+4=32 days.
11 January to 7 March is 21+28+7=56 days.
Total 88 days.
As 4 September 2018 is more than 180 days ago, that trip is no longer relevant.
Until 10 June, 11 January is less than 180 days ago, so the entire trip counts, but you can't spend 34 (90-56) days in Schengen before 10 June, so it's mostly irrelevant.
On 3 September 2019, 7 March 2019 will be 180 days ago, so after that the second trip doesn't matter either.
If you enter Schengen now (1 July), it will be the 57th day within the last 180 days, tomorrow will then be the 58th, and so on until the 9th (tuesday next week) which will be your 65th day within the last 180. But on the 10th, January 11 suddenly falls out of the 180 day window, so the 10th will also be your 65th day within 180 days. And until 2 September, every day will then be the 65th, after that the count starts increasing again, so 3 September will be the 66th, and so on. Until 27 September which will be the 90th day within the last 180 days.
As a stay from now until 27 September only comes to 89 days in my count, I must have made a minor mistake in the calculation. But the conclusion is clear, you can stay 90 days from today, as your previous stay will move out of the 180 day window during the stay.