twice the sum of a and b is thrice c

[math_celebrity]

twice the sum of a and b is thrice c

The sum of a and b:
a + b

twice the sum of a and b means we multiply the sum of a and b by 2:
2(a + b)

Thrice c means we multiply c by 3:
3c

The word is means equal to, so we set 2(a + b) equal to 3c:
2(a + b) = 3c