Twice a number increased by 5? in algebraic expression

2x+5 would be the equation

x is the "number" that is unknown, it's what's called a variable. Because you need two times a number (x) you put a coefficient of 2 in front of it, then simply add 5.

Examples with known variable values:

2 (4) + 5=13

2 (2) + 5=9