The second sheet of the spreadsheet linked above contains the scores of 50 students on 4 different exams, as well as weights that should be adjusted and used in the below question. What is the weighted mean of Student 21's exam scores when Exam 3 is weighted three times that of the other 3 exams?

Weights	1	1	1	1
Student	Exam1	Exam2	Exam3	Exam4
1	100	66	74	68
2	76	84	100	75
3	89	80	100	95
4	83	76	91	74
5	86	99	78	78
6	83	72	100	75
7	69	72	57	75
8	71	92	49	70
9	91	93	96	78
10	78	70	93	73
11	85	100	100	70
12	86	97	42	78
13	86	94	100	69
14	89	100	60	83
15	79	76	72	78
16	79	66	18	82
17	100	84	85	95
18	87	74	74	79
19	84	77	67	74
20	85	95	66	70
21	84	99	63	72
22	90	68	100	83
23	76	65	37	55
24	87	91	100	71
25	81	57	71	69
26	73	73	89	77
27	78	85	71	82
28	72	88	80	76
29	83	97	95	72
30	78	66	57	76
31	77	51	82	76
32	73	91	100	86
33	82	100	95	95
34	89	79	39	67
35	89	84	59	73
36	60	65	40	75
37	59	84	38	80
38	87	65	71	79
39	83	86	78	81
40	69	70	58	70
41	96	68	75	77
42	82	76	69	74
43	76	96	100	74
44	85	54	43	71
45	78	86	80	80
46	96	83	36	83
47	100	100	95	100
48	99	49	84	74
49	75	55	59	63
50	92	72	81	75