Let the number be x. "Three times a number increased by 10" is mathematically translated as
3x + 10
"is equal" is mathematically translated as twenty less than six times the number" is mathematically translated as
6x - 20
The whole sentence "Three times a number increased by ten is equal to twenty less than six times the number" is translated as
3x + 10 = 6x - 20
We now solve the above linear equation to find the number x
3x - 6x = - 20 - 10
- 3x = - 30
x = 10
Check answer
Three times a number increased by ten : 3 × 10 + 10 = 40
Twenty less than six times the number : 6 × 10 - 20 = 40