580.
1) 5/12·а + 7 при а = 4
5/12·4 + 7 = 5/3 + 7 = 1целая 2/3 +7 = 8 целых 2/3
2) 4/9·b + 2/3 при b = 3/4
4/9·3/4 + 2/3 = 1/3 + 2/3 = 1
3) 2/5 + 1 1/4·а при а = 1 3/5
2/5 + 1 1/4·1 3/5 =2/5 + 5/4 · 8/5 = 2/5 + 2 = 2 целых 2/5
4) 2 3/10·b + 1/2 при b = 2 1/2
2 3/10·2 1/2 + 1/2 = 23/10 · 5/2 +1/2 = 23/4 + 1/2 = 23/4 + 2/4 = 25/4 = 6 целых 1/4