the sides of a triangle are xcm,x+3cm and 10cm.if x is a whole number of cm,find the lowest value of x

that's inequalities ...

If the sides are a,b,c then the longest side, say, c obeys
a-b < c < a+b
So, we must have

x+3 - x < 10 < x+3+x
3 < 10 < 2x+3

10-x < x+3 < 10+x
10 < 2x+3 < 2x+10

10-(x+3) < x < 10+x+3
7 < x < x+13

Looks like 2x > 7, so x >= 4

That makes the sides 4,7,10