I don’t understand can someone please help.

Step-by-step explanation:

Remark

The red triangle has 1/3 the side  length of    the blue triangle. So the quick answer is the missing side of the blue triangle is 66

Now no one marking this, if they require work is going to accept that quick line of reasoning, so what you have to do is set up a proportion.

Equation (proportion)

57/19 = x / 22                        Cross multiply

Solution

57*22 = 19 * x                        Divide by 19

57*22/19 = x                          Divide 19 into 57 (which is 3)

3 * 22 = x

x = 66