Robbie is preparing for a marathon. Altogether, Robbie ran a total of 43 miles. How many miles did
Robbie run on Friday? Here is his training schedule:
• Monday: ran x miles.
• Tuesday: ran double the miles he ran on Monday.
• Thursday: ran half the miles he ran on Monday,
• Friday: ran triple the miles he ran on Monday morning plus 4 more miles in the evening.

Please show the equation to solve for it, the answer, and the steps of solving the equation. Thank you~​