I’m having trouble understanding this, if anyone could help me understand it I’d greatly appreciate it.

x = angle left of (4x+5) [ᴄᴏʀʀᴇsᴘᴏɴᴅɪɴɢ ᴀɴɢʟᴇs]

So, x + (4x+5) =180° [sᴜᴘᴘʟᴇᴍᴇɴᴛᴀʀʏ ᴀɴɢʟᴇs]

=> ˢᵒ ᵗʰᵉ ᵛᵃˡᵘᵉ ᵒᶠ ˣ ⁱˢ ᵉᵠᵘᵃˡ ᵗᵒ 35

First, let's define the number we are looking for as n.

So "half a number" is (1/2)×n

Therefore, "four less than" this would be: ((12)×n)−4

And if this is or, in other words, = to #17 we can write the equation:

((12)×n)−4=17

Solving for n while keeping the equation balanced gives:

((12)×n)−4+4=17+4

(12)×n=21

(21)×(12)×n=21×(21)

((21)×(12))×n=421

1×n=42

n=42