Did you test 2?
144/2=72 there is not a 1 in the units column so it cannot be correct.
You could just try all the possible answers, there are only 9 of them, 1 through 9 but better still, do it as I have below
\(let \;\;x=\triangle\)
\(\frac{144}{x}=10+x\\ 144=x^2+10x\\ x^2+10x-144=0\\ x=\frac{-10\pm\sqrt{100+576}}{2}\\ x=\frac{-10\pm\sqrt{676}}{2}\\ x=\frac{-10\pm26}{2}\\ x=-5\pm13\\ x = -18\;\;or\;\;8\)
but x is a 1 digit number so it is 8
\(\triangle \;\;is\;\;8\)
check: 144/8=18 there is a one in the tens column and an 8 in the units so it works.
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